28th Texas Symposium on Relativistic Astrophysics

13 Dec 2015, 16:00 → 18 Dec 2015, 17:10 Europe/Zurich

International Conference Centre Geneva

The 28th Texas Symposium on Relativistic Astrophysics will be held in Geneva, Switzerland, from December 13 to 18, 2015. It is organized by the Astronomy Department and the Physics Section of the University of Geneva. The Symposium will include both invited and contributed talks and posters.

The Texas Symposia on Relativistic Astrophysics are an impressive series of events where major astrophysical discoveries have been announced and discussed in the field related to relativistic theory of gravitation and cosmology, such as black-holes, quasars, neutron stars, X-ray binaries, gamma-ray bursts, particle acceleration, the cosmic background, dark matter and dark energy.

We are excited to welcome hundreds of international astrophysicists and physicists in Geneva, the home town of the LHC, to review remarkable discoveries and prospects, one century after the publication of General Relativity by Albert Einstein, and to bridge astrophysics with particle physics.

The Symposium will include morning plenary sessions and afternoon parallel sessions which will function as mini-symposia in each sub-field. The plenary sessions will consist of 30-45 min review talks. The afternoon sessions will feature oral (about 20 min) and poster contributions.

IUPAP Young Astrophysicist Awards 2014/2015

The winners will receive their awards and present their scientific achievements at the 28th Texas Symposium on Relativistic Astrophysics.

        Support astronomy in Nepal

The TEXAS symposium 2015 will use possibly remaining fund in its budget to help high-level education in physics and astronomy in Nepal. You have the possibility to contribute to that effort during the registration process.

 

Sponsors:

	International Union of Pure and Applied Physics			University of Geneva
	The Tomalla Foundation			Swiss National Science Foundation
	INTEGRAL Science Data Center			Center for Astroparticle Physics
	Swiss Institute of Particle Physics			Société Académique de Genève
	Swiss Society for Astrophysics and Astronomy
	République et Canton de Genève			Geneva Tourism & Conventions Foundation
	International Conference Centre Geneva
	Swiss International Air Lines

 

The Texas Syposium 2015 will be conducted in accordance with IUPAP principles. In particular, no bona fide scientist will be excluded from participation on the grounds of national origin, nationality, or political considerations unrelated to science.

proceeding_template.tex

Symposium Picture

Symposium Poster

Symposium Programme

Videos of the morning sessions

Videos of the public talk

Monday 14 December

08:30 → 09:00 Registration

09:00 → 09:35 Cover: Welcome opening

04_kunz.pdf

06_EarlyUniverse.pdf

11_GW.pdf

12_lensing.pdf

15_Binaries.pdf

15_PTA.pdf

19_VHE.pdf

20_Future.pdf

EarlyUniverseSummary.pdf

Texas2015_Session_Cosmic-Magnetic-Fields.pdf

09:00 Introduction

09:07 Welcome address by the Vice-Rector of the University of Geneva

Speaker: Prof. Jean-Marc Triscone (University of Geneva)

09:15 Einstein's Swiss Years

Speaker: Prof. Jan Lacki (University of Geneva)

presentation_lacki.pdf

Video

09:35 → 10:45 Plenary talks

09:35 First hundred years of GR: successes, status and prospects

General Relativity revolutionized the way we we thought about gravity. After describing briefly the key successes of GR and their impact, I will discuss the major conceptual challenges it faces today. I will conclude by outlining the prospective future directions of development, which hold the promise for deepening our understanding of the nature of gravity further.

Speaker: Prof. Thanu Padmanabhan (ICAA Pune)

Padmanabhan.pdf

Video

10:10 Relativistic effects in large-scale structure surveys

The distribution of galaxies provides a powerful way to probe the properties of our universe. In order to exploit this observable properly it is necessary to understand what we are really measuring when we look at the large-scale structure. Since our universe is not completely homogeneous and isotropic, we only see a distorted picture of our sky. In this talk, I will discuss the various relativistic effects that distort our observations. I will show that even though these effects complicate the interpretation of galaxy surveys, they are very useful since they contain information about the theory of gravity and can therefore be regarded as a new opportunity for future surveys.

Speaker: Camille Bonvin (CERN)

relativistic_bonvin.pdf

Video

10:45 → 11:20 Coffee break and poster session

11:20 → 12:30 Plenary talks

11:20 CMB temperature and polarisation anisotropies: a goldmine for cosmology.

Over the last two decades cosmic microwave background (CMB) anisotropies have revolutionised our view of cosmology. Generations of experiments have successively uncovered the amplitude of the temperature fluctuations at large scales, the existence of acoustic peaks in both temperature and polarisation and the small scale damping. These observations have now established a minimal cosmological model with unprecedented accuracy of its cosmological parameters. I will show how CMB temperature and polarisation anisotropies are powerful cosmological probes of the concordance model.

Speaker: Nabila Aghanim (Universite Paris Sud)

plenary_1120_Aghanim_CMB temperature and polarisation.pdf

plenary_1120_Aghanim_CMB temperature and polarisation.ppt

Video

11:55 CMB spectral distortions

Speaker: Prof. Rashid Sunyaev

plenary_1155_Sunyaev.pdf

Video

12:30 → 14:00 Lunch break

14:00 → 15:45 13 - Gamma-ray bursts

Convener: Luigi Piro (National Institute for Astrophysics - INAF)

14:00 Thermal emission in GRB 101219B

In recent years there has been growing evidence that emission from the photosphere of the jet contributes to the prompt emission in many GRBs. The photospheric emission is usually seen to coexist with a dominant non-thermal component. In this talk I will present an analysis of GRB 101219B, the second burst observed by Fermi GBM that is well described by pure blackbody emission. This burst also has a previously reported detection of a blackbody component at soft X-ray energies in the early afterglow observed by Swift. There is no smooth connection between the two blackbody components, ruling out the scenario that the late emission is due to high-latitude effects. The observed properties of the blackbody emission, together with the known redshift and our estimate of the radiative efficiency, makes it possible to calculate the properties of the jet within the standard fireball model. This yields an initial Lorentz factor of ~140 and a nozzle radius of ~ $3\times10^7$ cm. The latter value is close to the event horizon for a stellar-mass black hole and suggests that the jet has a relatively unobstructed path through the star.

Speaker: Dr Josefin Larsson (KTH Royal Institute of Technology)

jlarsson_101219b.pdf

14:21 Fitting gamma-ray burst prompt emission spectra with a model for subphotospheric dissipation

The prompt emission mechanism of gamma-ray bursts (GRBs) is still unknown. While GRB spectra are usually well fitted by the Band function, an empirically motivated, smoothly broken power law, this gives little understanding of the underlying radiation mechanism. In this talk I will present results from fitting a physical model to prompt GRB spectra observed by Fermi. The model simulates the scenario of dissipation of kinetic energy below the photosphere in a relativistically expanding fireball. It is based on the code by Pe’er et al. 2005 and includes Compton and Inverse Compton scattering, synchrotron emission as well as pair production/annihilation. The data are fitted using an Xspec table model created from a large number of simulations. Our initial results show that the model can provide good fits to different types of spectra, capturing spectral features not caught by the corresponding Band function fits. I will present our latest results from fitting the model and discuss the implications of our best-fit parameters.

Speaker: Björn Ahlgren (KTH Royal Institute of Technology)

13_1421_Ahlgren_Confronting GRB prompt emission.key.zip

13_1421_Ahlgren_Confronting GRB prompt emission.pdf

14:42 Signs of magnetic acceleration and multi-zone emission in GRB 080825C

The era of the Band function paradigm is ending, due in large part to the high-quality data provided by the Fermi Gamma-ray Space Telescope. Practically all bright GRBs detected by Fermi-LAT and GBM data show deviations from a pure Band function, most often due to extra spectral features being present. Understanding the physics of these components is necessary to reveal the acceleration and emission processes active in the highly relativistic outflows of GRBs. Unfortunately, the number of bright GRBs is limited and we therefore look for the presence of possible extra components in weaker GRBs, to enlarge the sample. Here we present signs of a new high energy component in GRB080825C. This component is different from those previously reported, and its high energy and temporal behaviour point to multi-zone emission models where the particle acceleration is due to magnetic reconnection in the jet.

Speaker: Elena Moretti (MPI Munich)

grb080825C_Moretti_Texas_symp.pdf

15:03 A new intrinsic intrinsic 3 parameter correlation in Gamma Ray Bursts

An analysis of 176 GRBs with known redshift observed by Swift which present afterglow plateau revealed a new tri-parameter correlation (Lpeak,Lx,T*a) where Lpeak is the peak luminosity in the prompt emission, Lx is the luminosity at the end of the plateau emission and T*a is the rest frame time at the end of the plateau emission. We have already proven the intrinsic nature of the Lx- T*a (Dainotti et al. 2013a) and the Lpeak-Lx correlation (Dainotti et al. 2015b) through the Efron & Petrosian (1992) method. We here show the intrinsic slope of this new correlation whose intrinsic scatter is 10% less than the one for the Lx-T*a correlation, therefore this new relation can be more useful as a cosmological tool. In addition, we show how the separation between categories of GRB-SNe, X-ray Flashes and short GRBs with extended emission are displayed in the 3D space. It is advisable to divide the categories before using this correlation for cosmological study. Finally, we also present the Lpeak-T*90 correlation, where T90 is the time where the 90% of the prompt emission is emitted between 5% and 95%. This correlation is weaker than the Lpeak-T*a one, thus favoring the choice of T*a as a preferred time as a third parameter in the 3D mentioned correlation.

Speaker: Maria Dainotti (Stanford University)

Review_Ginevra_2015.pdf

Review_Ginevra_2015.pptx

15:24 GRB polarization with the POLAR detector.

The POLAR detector will be launched together with the Tiangong 2 Chinese space station in the Summer of 2016 from Jiuquan Launch center. POLAR is a GRB polarimeter that will be able to measure GRB polarization degree with 10% precision for 10 GRB per year. POLAR detector has been build by a Chinese-Swiss-Polish collaboration. POLAR flight spare model has passed all qualification tests during 2014 and was tested and calibrated in a polarized beam facility in ESRF Grenoble. POLAR flight model has passed all acceptation level tests and was delivered to China in July 2015 for integration on Tiangong 2. GRB polarization measurements will help to validate or infirm the predictions of the different models of the GRB central engine. GRB polarization measurements are also interesting as probe of the quantum gravitation effects. POLAR can also be used to perform some Solar flare polarization measurements.

Speaker: Dr Nicolas Produit (Universite de Geneve (CH))

13_1524_Produit_GRB_polarization_with_the_polar_detector.pdf

14:00 → 15:45 15 - Binaries: HMXB

Convener: Alessandro Papitto

14:00 Multi-wavelength variability of the gamma-ray binary LS I +61 303 along the super-orbital period

Detected from radio to TeV gamma rays, the gamma-ray binary LS I + 61º303 is highly variable across all frequencies. Beside its variability due to the modulation of its emission due to the 26.496-day orbital period, the system also presents variability consistent with the so-called superorbital period, of 1667 days. We will present the latest data set of LSI +61º 303 taken with the Fermi Large Area Telescope and put it in a multi-wavelength context. Furthermore, we show for the first time that not only at GeV energies but also in other bands, the superorbital modulation is more prominently seen at orbital phases around apastron, whereas it does not introduce a visible change close to periastron. Finally, we present correlation studies between GeV, X-ray, optical, and radio data and comment on a physical, pulsar-based scenario which could explain the behavior of this enigmatic binary.

Speaker: Prof. Diego Torres (ICREA / Institute of Space Sciences)

15_1400_Torres_Multi wavelenght.pdf

15_1400_Torres_Multi wavelenght.pptx

14:26 Interacting pulsar winds in X-ray and gamma-ray binaries

The presence of a relativistic pulsar wind has been established in several X-ray binaries. The interaction of the pulsar wind with the stellar companion, stellar wind, or accretion disk can lead to peculiar signatures, most prominently the emission of high-energy gamma-rays. I will describe our efforts to model this interaction in order to translate gamma-ray observations into a better understanding of relativistic magnetized outflows.

Speaker: Guillaume DUBUS (IPAG CNRS/Université Grenoble Alpes)

dubus_texas_geneve.pdf

14:52 The gamma-ray monitoring of newly discovered Be/BH binary system MWC 656

MWC 656 is a Be star with a black hole (BH) companion, being the first and unique Be/BH binary system found. The detected X-ray counterpart implies that MWC 656 is, as well, the first Be/BH X-ray binary found. We carried out a search in archival AGILE data and found ten gamma-ray flares compatible with the position of the binary system, although no periodicity in the gamma-ray activity has been detected, so far. We report on the spectral fitting for both X-ray and gamma-ray data. The derived non-thermal X-ray luminosity of the system, together with radio luminosity upper limits, makes MWC 656 compatible with the radio/X-ray luminosity correlation found for LMXBs. MWC 656 is located at the level of the faintest detected LMXBs, thus suggesting that this correlation might also be valid for HMXBs with very low X-ray luminosities.

Speaker: Pere Munar-Adrover (INAF-IAPS)

15_1452_munaradrover_MWC_656_agile_texas_2015.key

15_1452_munaradrover_MWC_656_agile_texas_2015.pdf

15:18 Making the Heaviest Elemens in the Universe

The origin of the heavy elements made by the rapid neutron-capture process (”r-process”) is not fully understood, yet. Different sources have been proposed, e.g., core-collapse supernovae as well as neutron star mergers. - We discuss the production of r-process elements in three of these suggested sites: 1.the neutrino wind in core collapse supernovae, 2. jet ejecta from magneto-rotationally driven (MHD) supernovae, and 3. neutron star mergers, with respect to the predicted environment conditions and the uncertainties in nuclear input physics. This comes to the conclusion that regular core collapse supernovae cannot be the source of the heaviest r-process elements, there is a slight chance that minor contributions for medium-heavy r-process nuclei originate from them. - In a second step we utilize Europium (Eu) in old metal-poor stars as the most indicative element to trace the r-process production in galactic evolution, since it is dominantly made by the r-process and relatively easy to observe compared to other heavy r-process elements. We test the most important parameters affecting the chemical evolution of our Galaxy as a function of metallicity ([Fe/H]) with an inhomogeneous (not automatically mixed) model. These are (a) for neutron star mergers the coalescence time scale of mergers and the probability to experience such a merger event after two supernova explosions occurred and formed a double neutron star system, and (b) for the sub-class of MHD-supernovae their occurrence rate compared to standard supernovae. - The main results are the following: The observed [Eu/Fe] pattern in the Galaxy can be reproduced by a combination of neutron star mergers and MHD-supernovae as r-process sources. While neutron star mergers alone seem to set in at too high metallicities, MHD-SNe provide a cure for this deficiency at low metallicities. Furthermore, we confirm that local inhomogeneities can explain the observed large spread in the Eu abundances at low metallicities. We also predict the evolution of oxygen ([O/Fe]) as a function of metallicity, to test whether the spread in so-called α-elements for inhomogeneous models agrees with observations, and whether this provides either constraints on supernova explosion models and their nucleosynthesis or clues on mixing processes in the interstellar medium.

Speaker: Friedrich Thielemann (University of Basel)

texas_fkt_talk.pdf

14:00 → 15:45 08 - Cosmic microwave background

Convener: Antony Lewis (University of Sussex)

14:00 The POLARBEAR experiment probing the cosmic microwave background polarization

The B-mode polarization of the cosmic microwave background (CMB) is a unique window on fundamental questions in physics. The mass of the neutrinos and the properties of the dark energy affect the structure formation, the gravitational lensing exerted by these structures on CMB results in a B-mode signal at small scales. The large scales of the B-mode spectrum convey fundamental information on the primordial universe, such as the energy scale and other properties of inflation. As the sensitivity of the instruments has approached the level of the B-modes signal, its measurements have become of major interest in cosmology. At the forefront in this quest, POLABEAR is a ground based telescope located in the Atacama desert (Chile), at nearly 5200 m of altitude. With a 3.5 arcmin resolution and a 1274 polarization sensitive bolometers, POLABEAR has been observing three 10 deg$^2$ CMB patch at 150 GHz since 2012. Using the data of the first observational campaign, which ended in may 2013 POLABEAR provided indirect measurements of B-modes either via cross-correlation of its maps with the Herschel cosmic infrared background maps (on 4 $\sigma$ level), or from an analysis of 4-point moments of the polarization maps only (4.2 $\sigma$). A direct measurement of the B-mode power was also delivered finding an evidence (97.5 % c.l.) for non-zero sky power consistent with the predicted lensing B-mode signal. Furthermore, POLABEAR recently set new constraints on the cosmic birefringence and primordial magnetic fields. In this talk I will describe these results in detail as well as present the plans for the future of the POLABEAR experiment. POLABEAR 2 and the Simons Array will increase the sensitivity and have multiple frequency bands for a better rejection of the foreground signals.

Speaker: Davide Poletti

20151214_texas_symposioum_polarbear_poletti.pdf

14:25 The Quijote experiment: project overview and first results

The QUIJOTE (Q-U-I JOint TEnerife) experiment is a new polarimeter working in the frequency range 10-40 GHz, and designed to characterize the primordial B-mode anisotropy of the CMB polarization down to a sensitivity in the tensor-to-scalar ratio of r~0.05, and to measure the level of the polarization of low-frequency Galactic foregrounds (the synchrotron and the anomalous dust emissions). The project consists of two telescopes and three instruments which will survey a large sky area (20000 sq-deg) from the Teide Observatory (Tenerife) to provide Q and U maps of high sensitivy (1-3 µK/beam in a deeper region of 3000 sq-deg). The first telescope and the Multi-Frequency Instrument (MFI) are operative since November 2012 in the frequency range 10-20 GHz. The second telescope and two additional instruments, respectively at 30 and 40 GHz, are currently under construction. These two experiments will provide Q and U maps with a sensitivity better than 1 µK/beam. In this talk I will discuss the status of this project, its future goals, and will present the first results obtained with the MFI, with emphasis on the inferred limits on the polarization fraction of the anomalous dust emission, and on the characterization of the properties of the synchrotron polarization in various regions that we have observed.

Speaker: Dr Ricardo Génova Santos (Instituto de Astrofísica de Canarias)

08_1425_Genova-Santos_The_Quijote_experiment_project_overview_and.pdf

14:45 CMB spectral distortions: energy release versus photon injection

CMB spectral distortions caused by energy release in the early Universe create broad distortions that are usually described as superposition of mu-, y- and r-type distortions. These signals will allow us to gain new insights into the pre-recombination Universe, telling us about early-universe and particle physics. There is, however, another way to create distortions: by *photon injection*. One example is related to the hydrogen and helium recombination radiation emitted around *z*~1000, however, similarly decaying and annihilating particle scenarios or super-conducting strings should lead to copious photon production. The types of distortions that are created by photon injection show a much richer phenomenology than the classical mu and y distortions, as I will illustrate in my talk. This may provide additional ways of distinguishing different energy release mechanisms.

Speaker: Jens Chluba (Institute of Astronomy)

08_1445_Chluba_Cmb spectral distortions.key

08_1445_Chluba_Cmb_spectral_distortions.pdf

15:05 Cosmology with the Planck all-sky Compton parameter map

Clusters of galaxies are the largest bound structures in the Universe. Thus, they are observables of choice for cosmology both in terms of their aboundance and of their distribution on the sky. Clusters of galaxies can be observed at different wavelengths via their X-ray and radio emission as well as from the optical emission of their galaxies. In addition, they can be studied via the thermal Sunyaev-Zeldovich (tSZ) effect, which is the distortion of the CMB spectrum caused by the interaction of the CMB photons with the diffuse hot gas in the clusters. The Planck satellite, observing the sky at 9 frequencies from 30 to 857 GHz with a resoltuion from 40 to 4.5 arcmin, is particularly well adapted to the study of the tSZ effects in clusters of galaxies. Using dedicated component separation methods and by combining the Planck data at all frequencies we have obtained the first all-sky map Compton parameter map of the tSZ emission. We present here a detailed characterisation of this map in terms of noise properties and systematics. We also present the angular power spectrum and non-gaussian properties of the map. Finally, these are used to obtain constraints on cosmological parameters. We find good agreement with the results obtained from cluster number counts and in weak tension with CMB ones. We briefly indicate how the latter can be understood in terms of cluster physics.

Speaker: Dr Juan Francisco Macias-Perez (LPSC)

ymap_maciasperez.pdf

15:25 High-resolution SZ cartography of clusters of galaxies with NIKA ath the IRAM 30-m telescope

Thermal Sunyaev-Zeldovich effect (tSZ) is a powerful probe that has been proved to be complementary with respect to traditional methods of cluster detection (e.g. X-ray, optical). Previous arcmin resolution tSZ observations (e.g. SPT, ACT and Planck) only allowed detailed studies of the intra cluster medium morphology for low redshift clusters (z < 0.2). Thus, the development of precision cosmology with clusters requires high angular resolution observations to extend the understanding of galaxy cluster towards high redshift. NIKA2 is a wide-field (6.5 arcmin field of view) dual-band camera, operated at 100 mK and containing ~ 5000 KID (Kinetic Inductance Detectors), designed to observe the millimeter sky at 150 and 260 GHz, with an angular resolution of 18 and 12 arcsec respectively. The NIKA2 camera will be installed on the IRAM 30-m telescope (Pico Veleta, Spain) in September 2015. The NIKA2 tSZ observation program will allow us to observe a large sample of clusters (50) at redshifts between 0.5 and 1. As a pathfinder for NIKA2, several clusters of galaxies have been observed at the IRAM 30-m telescope with the NIKA prototype to cover the various configurations and observation conditions expected for NIKA2. I will present recent tSZ observations of clusters of galaxies with the NIKA prototype at the IRAM 30-m telescope together with the forthcoming tSZ observation program with the NIKA2 camera.

Speaker: Frédéric MAYET (CNRS)

08_1525_Frederic Mayet-High resolution SZ cartography.pdf

08_1525_Frederic Mayet-High resolution SZ cartography.pptx

proc-mayet2015.pdf

14:00 → 15:45 06 - Early universe

Convener: Daniel G. Figueroa (CERN)

14:00 Exotic Rotational Correlations in Emergent Quantum Geometry

It is proposed that small amplitude, coherent rotational fluctuations arise from the emergence of nearly-classical non-rotating inertial frames from Planck scale quantum elements. An exact form is calculated for Planck scale correlations in the signal of a Sagnac type interferometer, where the light path encloses a large area of arbitrary shape, normalized using area quantization from Loop Quantum Gravity. It is conjectured that such Planck scale rotational fluctuations, entangled with the strong interaction vacuum, may determine the value of the cosmological constant. Cosmic acceleration may be viewed as centrifugal acceleration by rotational fluctuations of the matter vacuum. An experiment concept is sketched, based on a reconfiguration of the Fermilab Holometer.

Speaker: Craig Hogan (U. Chicago and Fermilab)

QuantumTwistsHoganTexas.pdf

14:21 Creation of Emergent Universe with Wormholes

Emergent universe (EU) scenarios describe the evolution of a static Einstein universe in the infinite past whereby certain problems associated with the big-bang singularity can be circumvented. A flat universe composed of interacting fluids with a non-linear equation of state within the EU scenario leads to a viable cosmological model accommodating the presently observed accelerating era, as well. In the present work we focus on the origin of such a EU scenario. By investigating the very early universe in the presence of gravitational instanton solutions, we show how a static Einstein universe emerges, leading to a cosmologically viable EU scenario in the framework of massive gravity. Our analysis leads to certain constraints on the model parameters for the feasibility of such a scenario.

Speaker: Dr. Bikash Chandra PAUL (University of North Bengal)

BCP-texas.pdf

14:42 A Cyclic Universe alternatively dominated by matter and antimatter

It was recently suggested that what we call dark matter and dark energy, can be explained as the local and global effects of the gravitational polarization of the quantum vacuum by the immersed Standard Model matter. This result appears as the consequence of the working hypothesis that by their nature quantum vacuum fluctuations are virtual gravitational dipoles. Here, we argue that, as a consequence of the same hypothesis, we may live in a cyclic universe with cycles alternatively dominated by matter and antimatter. At least mathematically there is no the initial singularity, there is no need for the cosmic inflation and there is an amusing explanation of the matter-antimatter asymmetry in the universe: our universe is dominated by matter because the previous cycle was dominated by antimatter (and the next cycle would be dominated by antimatter again).

Speaker: Dragan Hajdukovic (Institute of Physics, Astrophysics and Cosmology)

CU-Hajduk.proc.pdf

CyclicUniverse-Hajdukovic.pdf

15:03 3D Quantum Bubble Collisions

First-order phase transitions proceed through the nucleation and subsequent collision of bubbles. In false vacuum eternal inflation, such collision events are ubiquitous and provide a possible avenue to observationally test the multiverse. They also play an important role in early high temperature phase transitions. I will present results for the full three-dimensional nonlinear dynamics of pairwise bubble collisions, including for the first time the effects of (initially small) quantum fluctuations. This significantly extends the standard treatment of bubble collisions. In the standard approach, the field profile is assumed to possess a spatial SO(2,1) symmetry and the dynamics reduces to one spatial dimension. However, quantum fluctuations break the assumed symmetry and cannot be studied in the symmetry based formalism. I will show that accounting for the dynamics of these fluctuations leads to a complete breakdown of the SO(2,1) symmetry in a wide class of potentials. Initially, the fluctuations experience a linear parametric instability, which can be interpreted as an inhomogeneous version of Bogoliubov particle production. At the onset of mode-mode coupling, the bubble walls in the collision region dissolve, leaving behind a population of localized oscillating blobs of field known as oscillons. This has implications for the production of gravitational waves or black holes during bubble collisions.

Speaker: Jonathan Braden (University College London)

bubble_cosmo.pdf

15:24 Born-Infeldizing gravity

In order to regularize the energy of point-like charged particles, Born and Infeld introduced a modification of the Maxwell lagrangian that naturally imposes an upper bound on electromagnetic fields. This approach was later taken by Deser and Gibbons to propose an analogous modification for gravity. I will review these ideas and discuss a scenario where inflation could be supported by a set of massive particles within the context of these theories.

Speaker: Lavinia Heisenberg (ETHZ - ETH Zurich)

BornInfeldGeneva2015.pdf

14:00 → 15:45 02 - Exact solutions

Convener: Mustapha Ishak (The University of Texas at Dallas)

14:00 Modelling inhomogeneous cosmologies with Numerical Relativity

Building accurate, multi-scale models of the Universe is a complex but necessary task in the era of precision cosmology, when observational data demands a thorough understanding of all effects which are expected to contribute at the 1% level, among which the full role of General Relativity. This task has recently been tackled with a variety of approaches, which range from the study of toy models [1], to analytical expansions [2] and hybrid analytical-numerical methods where relativistic effects are superimposed on classical, Newtonian N-body systems [3][4][5]. In this presentation, I will describe recent work carried out in Numerical Relativity to describe the relativistic Universe exactly, integrating Einstein’s equation in three dimensions. This approach is the only one that can account for the full extent of the theory, and has already yielded significant results in several scenarios, such as black-hole lattices [6] and scalar-field collapse in cosmological settings [7]. References: [1] Korzyński, M., “Nonlinear effects of general relativity from multiscale structure”, http://arxiv.org/abs/1412.3865 [2] Bruneton J.-P. and Larena, J., “Dynamics of a lattice Universe: The dust approximation in cosmology”, http://arxiv.org/abs/1204.3433 [3] Bruni, M., Thomas, D. and Wands, D., “Computing General Relativistic effects from Newtonian N-body simulations: Frame dragging in the post-Friedmann approach”, http://arxiv.org/abs/1306.1562 [4] Adamek, J. et al, “N-body methods for relativistic cosmology”, http://arxiv.org/abs/1408.3352 [5] Adamek, J. et al, “General relativity and cosmic structure formation”, http://arxiv.org/abs/1509.01699 [6] Bentivegna, E. and Korzynski, M., "Evolution of a periodic eight-black-hole lattice in numerical relativity”, http://arxiv.org/abs/1204.3568 [7] Torres, J. M. et al, “Cosmological nonlinear structure formation in full general relativity”, http://arxiv.org/abs/1409.7953

Speaker: Dr Eloisa Bentivegna (Università degli Studi di Catania)

bentivegna.key

bentivegna.pdf

proceeding.pdf

14:21 Solving the Einstein-Maxwell Equations for the Dispersive Propagation of Light during Mixmaster Kasner Epochs and other Anisotropic Early-Universe Models

The pre-homogenized very early universe generically experiences Mixmaster-like behavior as it approaches the Big Bang, featuring a sequence of anisotropically expanding Kasner epochs. Beyond drawing general conclusions about the transport of mass-energy in such environments, it would be helpful to obtain as much information as possible about the detailed propagation of energy in rapidly and nonadiabatically expanding metrics for which the geometrical optics approximation substantially breaks down. Here we solve for the propagation of (“test particle”) electromagnetic fields through background spacetimes with various sets of Kasner expansion indices. In solving the Einstein-Maxwell equations, we obtain independent fourth-order differential equations for each of the electric and magnetic fields which can be individually solved for the amplitudes and phase velocities of the fields to yield interesting information about how they are parametrically driven by the asymmetrically expanding early universe. Furthermore, we consider other anisotropic (and non-vacuum) models, including metrics related to the Vaidya and Szekeres-Szafron solutions, which include inhomogeneity as well as anisotropy.

Speaker: Brett Bochner (Hofstra University)

Bochner--Exact_Solns_Par_Session--28th_Tex-in-Geneva.pdf

Proceedings--28_Tex_in_Geneva--Bochner.pdf

14:42 Backrection of voids in a Friedman background with constant w equation of state.

I introduce new exact solutions of the Szekeres-Szafron type describing voids on a Friedmann-Roberson-Walker background with w=constant equation of state. At least in the linear regime the inhomogeneities can be thought of as large scale perturbations of the background. Using these exact solutions the averaged quantities of the Buchert scheme can be calculated exactly. I show that in general the late-time evolution is dominated by the voids: these back-react in such a way that the average expansion is significantly different from the background one, I will describe how.

Speaker: Marco Bruni (University of Portsmouth)

02_1442_Bruni_BckreactionofvoidsinaFRWbackgroundwithconstantWeqofstate.key

02_1442_Bruni_BckreactionofvoidsinaFRWbackgroundwithconstantWeqofstate.pdf

15:03 Lense-Thirring precession in strong gravitational fields

The exact Lense-Thirring precession frequencies for Kerr, Kerr–Taub–NUT,Taub–NUT, Plebanski-Demianski spacetimes are explicitly derived. Remarkably, in the case of the zero angular momentum Taub–NUT spacetime, the frame-dragging effect is shown not to vanish, when considered for spinning test gyroscopes. In the case of the interior of the rotating neutron stars, the exact frame-dragging rate monotonically decreases from the center to the surface along the pole and along the equatorial distance, it decreases initially away from the center, becomes negligibly small well before the surface of the neutron star, rises again, and finally approaches to a small value at the surface. The appearance of a local maximum and minimum in this case is the result of the dependence of frame-dragging frequency on the distance and angle. Moving from the equator to the pole, it is observed that this local maximum and minimum in the frame-dragging rate along the equator disappear after crossing a critical angle. It is also noted that the positions of the local maximum and minimum of the frame-dragging rate along the equator depend on the rotation frequency and central energy density of a particular pulsar. The same anomaly can also be found in the case of Kerr–Taub–NUT spacetime but it is along the pole. Presently, direct observation of the Lense-Thirring precession of a classical or quantum spin vector relative to local inertial frames dragged along a timelike curve in any stationary spacetime is impossible in the presence of strong gravitational fields. Analogue models of black holes offer an alternative option of its indirect measurement in a comparatively accessible laboratory setup. We deduce precise estimate of the angular velocity of precession of a test spin outside the ergoregion of a fluid mechanical rotating “dumb hole” in acoustic spacetimes. It is our hope that with present technological expertise in manipulating analogue black holes, experimentalists will be able to successfully verify our estimate and hence, more importantly, the predicted strong gravity Lense- Thirring effect.

Speaker: Dr Chandrachur Chakraborty (Tata Institute of Fundamental Research , Mumbai , INDIA)

chakraborty_proc.pdf

15:24 Inhomogeneous conformally flat models of the universe

I will discuss the benefits of the conformally flat inhomogeneous pressure models of the universe. Then, I will present the results of checking these models against supernovae data for off-centers observers and against other data (BAO, CMB) for the centrally-placed observers. I will also comment on the possible advantage of these models in view of the recently given Green and Wald conditions for backreaction to mimic dark energy. 1. A. Balcerzak, M.P. Dąbrowski, and T. Denkiewicz, Off-center observers versus supernovae in inhomogeneous pressure universes, Astroph. Journ. 792, 92-99 (2014). 2. A. Balcerzak, M.P. Dąbrowski, T. Denkiewicz, D. Polarski, D. Puy, A critical assessment of some inhomogeneous pressure Stephani models, Phys. Rev. D91, 083506 (2015). 3. A. Balcerzak, M.P. Dąbrowski - in progress.

Speaker: Mariusz Dabrowski (University of Szczecin)

02_1524_MariuszDabrowski_Inhomogeneousconformallyflatmodelsoftheuniverse.pdf

14:00 → 15:45 18 - Gal. accel. & pulsars: Galactic accelerators

Convener: Marco Tavani (INAF)

14:00 H.E.S.S. Observations of the Large Magellanic Cloud

The Large Magellanic Cloud (LMC) is an irregular satellite galaxy of the Milky Way, which has been observed extensively at Very-High-Energy (VHE) gamma-rays with the H.E.S.S. telescopes, obtaining a deep exposure of 210 hours. In this talk we will present the results of this campaign. Besides the already known PWN N 157B, these observations establish significant VHE gamma-ray emission from the super-bubble 30 Dor C and show evidence for emission from the supernova remnant N 132D. It is the first unambiguous detection of gamma rays from a super-bubble and for the first time individual cosmic-ray accelerators are identified in an external galaxy. Contrary to theoretical expectations, VHE gamma-ray emission is not detected from SN 1987A. We will discuss these three objects, representing the high-energy tip of the VHE gamma-ray source population in the LMC, as possible cosmic-ray accelerators, and compare them with similar systems in our Galaxy. Further discoveries can be expected with more sensitive surveys of the LMC in gamma-rays, for instance with the Cherenkov Telescope Array.

Speaker: Nukri Komin (Wits University)

18_1400_Komin_LMC_HESS.pdf

18_1400_Komin_LMC_HESS.ppt

14:20 Galactic Science with the Cherenkov Telescope Array

CTA is the next generation ground based gamma-ray observatory planned to start operations before the end of the decade. With tens of telescopes on sites in both hemispheres, it will allow probing the Milky Way with an unprecedented sensitivity and angular resolution, in the energy domain from a few tens of GeV to a few hundreds of TeV. I will review the CTA Galactic science program ranging from the Galaxy plane to the LMC surveys, including selected deep field studies, transients monitoring and the long standing search for pevatrons.

Speaker: Dr Thierry Stolarczyk (IRFU/SAp,CEA Saclay, 91190 Gif-sur-Yvette (FR))

Texas2015-GalacticScienceCTA-ThStolarczyk.pdf

14:45 Modeling Bright Gamma-ray and Radio Emission from Fast Cloud Shocks at Middle-aged SNRs

Recent observations by the Large Area Telescope (LAT) onboard the Fermi satellite have revealed bright gamma-ray emission from middle-aged supernova remnants (SNRs) inside our Galaxy. These remnants which also possess bright non-thermal radio shells are often found to be interacting directly with surrounding gas clouds. We explore the non-thermal emission mechanism at these dynamically evolved SNRs by constructing a hydrodynamical model. Two scenarios of particle acceleration, either a re-acceleration of Galactic cosmic rays (CRs) or an efficient nonlinear diffusive shock acceleration (NLDSA) of particles injected from downstream, are considered. Using parameters inferred from observations, our models are contrasted with the observed spectra of SNR W44. For the re-acceleration case, we predict a significant enhancement of radio and GeV emission as the SNR undergoes a tran- situation into the radiative phase. If sufficiently strong magnetic turbulence is present in the molecular cloud, the re-acceleration scenario can explain the observed broadband spectral properties. The NLDSA scenario also succeeds in explaining the gamma-ray spectrum but fails to reproduce the radio spectral index. Efficient NLDSA also results in a significant post-shock CR pressure that limits the cooling compression and prevents the formation of a prominent dense shell. Some other interesting differences between the two models in hydrodynamical behavior and resulting spectral features are illustrated in detail.

Speaker: Dr Shiu Hang (Herman) Lee (ISAS/JAXA)

SHLee_2015.pdf

SHLee_proc_2015.pdf

15:05 Multiwavelength observations of gamma-ray loud binaries

Gamma-ray loud binaries are are a recently identified class of X-ray binaries in which interaction of an outflow from the compact object (black hole or neutron star) with the wind and radiation emitted by a companion star leads to the production of very-high energy (VHE) gamma-ray emission. Only five systems have been firmly detected so far as persistent or regularly variable TeV gamma-ray emitters. Detailed studies of the broadband spectral and timing properties of these sources are crucial for understanding the nature of these peculiar objects. In my talk I will review the outcome of extensive multiwavelength observations of the 2014 PSR B1259-63 periastron passage, which shed a light on the nature of the puzzling GeV flare from the system, and also discuss what can we learn from the numerous X-ray observations of LSI +61 303 performed the last decade by SWIFT, Suzaku, XMM and Chandra satellites.

Speaker: Maria Chernyakova (DCU)

18_1505_Chernyakova_Multiwavelenght_observation_of_gammaray_loud_binaries.pdf

15:25 Particle acceleration in Eta Carinae: the expected and unexpected

The Fermi Large Area Telescope (LAT) observed for the first time ever two consecutive $\eta$Carinae periastron passages. The large field of view of the instrument, its performing sensitivity and homogeneous exposition offers a continuous observation above 100 MeV of the $\eta$Carinae region on the last 7 years. $\eta$Carinae is a binary system hosted in the Carina nebula. Its luminous blue variable and O stars emit dense and high-velocity gaseous winds that make this system a promising particle acceleration site from which very high energy $\gamma$-ray emission can be expected. No other instruments before Fermi-LAT have ever detected the high energy emission coming from $\eta$Carinae in 2 consecutive periastron passages. A maximum likelihood analysis on the recent 7-year data of the Carina region clearly detects an high energy emission above 10 GeV during both periastron passages ($>5\sigma$) from a $95\%$ c.l. location strongly in agreement with the nominal position of $\eta$Carinae. A spectral analysis gives faint hints of an hardening of the spectral index immediately before both periastron passages. Contrarily to the expectation that the closeness of the two stars could increase the efficiency of the outflow enhancement into particle acceleration, a temporal analysis indicates that the flux does not show a strong periodicity. $\eta$Carinae system with its spectral variation and lightcurve represents a very good candidate to test and constraints future acceleration models for colliding wind binaries.

Speaker: Matteo Balbo (Université de Genève)

18_1525_Balbo_Particle_acceleration_in_eta_carinae.pdf

14:00 → 15:45 07 - Large scale structures

Convener: Vincent Desjacques

14:00 A relativistic approach to large-scale structure

As high-redshift galaxy surveys probe ever larger volumes with increasing accuracy there is renewed interest, and some concern, about how the standard results derived within the standard Newtonian approach to large-scale structure should be understood within a relativistic framework. How and when do Newtonian results need to modified? Relativistic corrections arise in several ways. For instance, the nonlinear constraint equations of general relativity impose different non-Gaussian initial conditions on the primordial density field in specific gauges. However we need to define the spatial and temporal gauge being used in our theoretical models in order to make physical predictions on cosmological scales. As an example, I will show how we may interpret standard N-body simulations most simply as evolution in a specific “N-body gauge”, at least to first order in general relativity. I will also discuss some outstanding issues beyond linear perturbation theory.

Speaker: David Wands (University of Portsmouth)

07_1400_David Wands-Relativistic approach to LSS-actual.pdf

14:21 Relativistic effects and primordial non-Gaussianity in the matter density fluctuation

We present the third-order analytic solution of the matter density fluctuation in the proper-time hypersurface of nonrelativistic matter flows by solving the nonlinear general relativistic equations. The proper-time hypersurface provides a coordinate system that a local observer can set up without knowledge beyond its neighborhood, along with physical connections to the local Newtonian descriptions in the relativistic context. The initial condition of our analytic solution is set up by the curvature perturbation in the comoving gauge, clarifying its impact on the nonlinear evolution. We compute the effective non-Gaussian parameters due to the nonlinearity in the relativistic equations. With proper coordinate rescaling, we show that gravity respects the equivalence principle the equivalence principle is respected and the relativistic effect vanishes in the large-scale limit.

Speaker: Jaiyul Yoo (University of Zurich)

07_1421_Alvise_Raccanelli_Texas.key.zip

07_1421_Alvise_Raccanelli_Texas.pdf

14:42 Relativistic effects with cross-correlations

I will discuss the galaxy clustering in a relativistic framework in terms of observable quantities, i.e angles and redshifts. A relativistic description includes terms beyond the Kaiser approximation (doppler effects and galaxy evolution), gravitational potentials and integrated terms (cosmic magnification, integrated Sachs-Wolfe and Shapiro time-delay). These terms are currently neglected, but they might play a role in future surveys which probe larger scales. I will show that by correlating different probes, or by using the so-called multi-tracer technique, some relativistic effects could give a non-negligible contribution to the galaxy clustering observables.

Speaker: Enea Di Dio (OATs-INAF)

DiDio_Texas_Geneva.pdf

15:03 Probing violations of slow-roll inflation at the largest observable scales with future galaxy surveys

The predictions of the simplest inflationary models, such as a flat Universe and Gaussian adiabatic perturbations with a red tilt, provide a remarkable good fit to the most recent measurements of CMB temperature and polarization anisotropies. Nevertheless, deviations from a simple power-law spectrum provide a better fit to Planck temperature anisotropies data, in particular on the largest scales, i.e. at $k < 0.008\ Mpc^{-1}$, although at a non-statistical significant level because of cosmic variance. We study the capability of future galaxy surveys as EUCLID and other experiments to distinguish possible deviations from a simple power-law for primordial perturbation on these large scales.

Speaker: Mario Ballardini (University of Bologna)

ProbeFeatures_proc.pdf

15:24 Tomographic lensing constraints with galaxy clustering

We investigate how well the lensing potential can be measured tomographically with future galaxy surveys using their number counts. Such a measurement is a consistency test of the standard ΛCDM framework. Based on galaxy angular-redshift power spectra, our analysis suggests that the survey can measure the amplitude of the lensing potential at the same level of precision as other standard ΛCDM cosmological parameters. We further discuss how the lensing signal affects the angular-redshift bispectra.

Speaker: Francesco Montanari (Universite de Geneve (CH))

07_FrancescoMontanari_Tomographic lensing constraints with galaxy clustering.pdf

14:00 → 15:45 04 - Dark energy

Convener: Martin Kunz (Universite de Geneve (CH))

14:00 High redshift BAO from BOSS to eBOSS

The first detection of Baryon Acoustic Oscillations (BAO) in the correlation function of the galaxy density field by Eisenstein et al. (2005) and Cole et al. (2005) set a milestone in the era of precision cosmology, providing a new, independent method for the measurement of cosmological distances. The Baryon Oscillation Spectroscopic Survey (BOSS), one of the experiment of the third generation of the Sloan Digital Sky Survey (SDSS-III), produced the first high redshift (z=2.34) measurement of the BAO scale using the Lyman-alpha forest of quasars as a tracer of the underlying matter density field (Delubac et al. 2015). During this talk, I will review the analysis that led to this measurement as well as present new results using the final dataset of BOSS. I will present the cosmological implications of this measurement when combined with other results (Aubourg et al. 2015) including constraints on the Dark Energy. I will pursue by introducing the extended Baryon Oscillation Spectroscopic Survey (eBOSS) of the fourth generation of the SDSS (SDSS-IV) that uses the same facility as BOSS, and show how it will tighten the constraints on our cosmological model.

Speaker: Dr Timothée Delubac (Ecole Polytechnique Fédérale de Lausanne)

04_1400_Timothee_High_redshift_BAO_from_Boss_to_eboss.pdf

14:27 Tracing dark energy with quasars.

The discovery of the accelerated expansion of the Universe lead to the concept of dark energy. This is one of the most interesting topic in modern relativistic astrophysics. Precise measurement of this effect is a key to understand the nature of this medium, and we need good probes to do that. Quasars appears as an ideal candidate for this purpose as these objects are highly luminous and detected in wide range of redshift (0< z <7). They can be used to track the history of the expansion of the Universe (Watson et al. 2011, Czerny et al. 2013, Marziani & Sulentic 2013, 2014; Wang et al. 2013; Hoenig 2014; Yoshii et al.2014). I will describe new encouraging results from the dedicated spectroscopic monitoring being currently performed by our team using Mg II line. Quasars are not standard candles so their use is based on determination of their two parameters redshifts and, independently, absolute luminosities. Absolute luminosity, combined with the observed luminosity, allows to obtain the luminosity distance to an individual quasar. Thus for each source we have independently the distance and the velocity (from redshift), i.e. the Universe expansion rate. The method is essentially equivalent to the use of the SN Ia but it is important to have several independent tracers as each of them have specific, hard to estimate, systematic errors. Specific advantage of quasars is, they do not show significant evolution of their properties with redshift which is likely a serious problem for SN Ia. The project in which I am involved uses the intermediate redshift quasars observed with 11-m Southern African Large Telescope. Determination of the quasar absolute luminosity comes from the measurement of the time delay between one of the strong emission lines and a continuum. MgII line is suitable for sources with redshift between 0.4 and 1.5, where this strong line moves to optical band of the spectrum. High-quality spectra from SALT allow for a very detailed modeling of the line shape and remove potential sources of the systematic errors. I will summarize all pros and cons of various recently proposed quasar-based methods of the measurement of the dark energy content of the Universe.

Speaker: Justyna Średzińska (Nicolaus Copernicus Astronomical Center PAS)

14:53 Measuring cosmological parameters with GRBs: status and perspectives

Given their huge isotropic-equivalent radiated energies, up to more than 10$^{54}$ erg released in a few tens of seconds, and their redshift distribution extending up to more than z = 9, Gamma-Ray Bursts (GRB) are in principle a powerful tool for measuring the geometry and expansion rate of the Universe. In the recent years, several attempts have been made to exploit the correlation between the photon energy at which the $\nu$F$\nu$ spectrum peaks ("peak energy") and the radiated energy (or luminosity) for "standardizing" GRBs and use them as tools (complementary to other probes like SN Ia, BAO and the CMB) for the estimate of cosmological parameters. These studies show that already with the present data set GRBs can provide a significant and independent confirmation of $\Omega_M$ $\sim$ 0.3 for a flat $\Lambda$CDM universe and that the measurements expected from present and next GRB experiments (e.g. Swift, Fermi/GBM, SVOM, CALET/GBM, UFFO) will allow us to substantially improve the constraints on $\Omega_M$ and $\Omega_\Lambda$, and, in particular, to get unique clues on dark energy properties and evolution.

Speaker: Lorenzo Amati (INAF - IASF Bologna)

Amati_texas15_cosmo_short.pdf

15:19 The m-z relation for type Ia supernovae, locally inhomogeneous cosmological models, and the nature of dark matter

The magnitude-distance relation for type Ia supernovae is one of the key pieces of evidence supporting the cosmological "concordance model". The resulting constraints on the cosmological parameters are often derived under the idealized assumption that the universe is perfectly homogeneous (at least as far as light propagation is concerned). However, we know that the universe is not homogeneous on small scales, and we know that such local inhomogeneities affect light propagation and hence distances which depend on angles, such as the luminosity distance. What does this mean for constraints on cosmological parameters derived from the magnitude-distance relation for type Ia supernovae? And, conversely, what does the fact that these constraints, when locally homogeneity is assumed, agree with other constraints mean for the nature of dark matter?

Speaker: Mr Phillip Helbig (*)

HELBIG_TEXAS2015_PROC.PDF

HELBIG_TEXAS2015_TALK.PDF

The m-z relation for type Ia supernovae, locally inhomogeneous cosmological models, and the nature of dark matter

15:45 → 16:15 Coffee break and poster session

16:15 → 18:45 13 - Gamma-ray bursts

Convener: Luigi Piro (National Institute for Astrophysics - INAF)

16:15 Using Gamma-Ray Bursts as Cosmological Probes

Although they are not standard candles, gamma-ray bursts (GRBs) are quite definitely cosmological objects, with some of the highest redshifts observed. The problem remains how to use GRB observables to construct a usable Hubble diagram. Several correlations between observables and the energetics have been noted, e.g. Amati et al. (2002) and Yonetoku et al. (2004), but it is not clear whether these suffer selection effects. I will discuss recent progress toward understanding the origin of these correlations that opens a road towards the GRB Hubble diagram.

Speaker: Rob Preece (University of Alabama in Huntsville)

13_1615_Preece_Using GRB for cosmology.pdf

16:35 Shedding light on the early Universe with THESEUS

The Transient High Energy Sky and Early Universe Surveyor (THESEUS) is a mission concept developed by a large international collaboration aimed at exploiting Gamma-Ray Bursts for investigating the early Universe. The main scientific objectives of THESEUS include: investigating the star formation rate and metallicity evolution of the ISM and IGM up to redshift 10, detecting the first generation (pop III) of stars, studying the sources and physics of re-ionization, detecting the faint end of galaxies luminosity function. These goals will be achieved through a unique combination of instruments allowing GRB detection and arcmin localizaiton over a broad FOV (more than 1sr) and an energy band extending from several MeVs down to 0.3 keV with unprecedented sensitivity, as well as on-board prompt (few minutes) follow-up with a 0.6m class IR telescope with both imaging and spectroscopic capabilities. Such instrumentation will also allow THESEUS to unveil and study the population of soft and sub-energetic GRBs, and, more in geeneral, perform monitoring and survey of the X_ray sky with unprecedented sensitivity.

Speaker: Lorenzo Amati (INAF - IASF Bologna)

Amati_texas15_theseus_short.pdf

16:55 An External Shock Origin of GRB 141028A

The prompt emission of the long, smooth, and single-pulsed gamma-ray burst, GRB 141028A, is analyzed under the guise of an external shock model. First, we fit the gamma-ray spectrum with a two-component photon model, namely synchrotron+blackbody, and then fit the recovered evolution of the synchrotron vFv peak to an analytic model derived considering the emission of a relativistic blast-wave expanding into an external medium. The prediction of the model for the vFv peak evolution matches well with the observations. We observe the blast-wave transitioning into the deceleration phase. Further we assume the expansion of the blast-wave to be nearly adiabatic, motivated by the low magnetic field deduced from the observations. This allows us to recover within an order of magnitude the flux density at the vFv peak, which is remarkable considering the simplicity of the analytic model. Under this scenario we argue that the distinction between *prompt* and *afterglow* emission is superfluous as both early and late time emission emanate from the same source. While the external shock model is clearly not a universal solution, this analysis opens the possibility that at least some fraction of GRBs can be explained with an external shock origin of their prompt phase.

Speaker: Dr J. Michael Burgess (KTH Royal Institute of Technology)

texas2015.key

texas2015.pdf

17:15 Signs of Blandford & Znajek mechanism in GRB afterglow lightcurves.

According to Blandford & Znajek (1977), the spin energy of a rotating black hole can be extracted electromagnetically, should the hole be endowed with a magnetic field supported by electric currents in a surrounding disk. We argue that this can be the case for the central engines of GRBs and we show that the duration of the burst depends on the magnetic flux accumulated on the event horizon of the black hole. We show that in several GRBs the theoretical curve of black hole spin down follows closely the energy flux (lightcurve). As a result we estimate the magnetic field strength at the vicinity of the black hole. Thus, we conclude that these GRBs have outflows with ordered magnetic fields and we estimate the field strength throughout the jet.

Speaker: Antonio Nathanail

13_1715_Nathanail_Signs of blandford and znajek mechanism.pdf

13_1715_Nathanail_Signs of blandford and znajek mechanism.ppt

17:35 Constraining emission mechanisms in gamma-ray bursts using spectral width

The emission processes active in the highly relativistic jets of gamma-ray bursts (GRBs) remain unknown. The spectra are usually well-fit by the Band function, an empirically motivated smoothly-broken power law, yet this gives little understanding of the underlying radiation mechanisms. In this talk we propose a new measure to describe spectra: the width of the EFE spectrum, a quantity dependent only on finding a good fit to the data. We apply this to the full sample of peak flux GRB spectra observed by CGRO/BATSE combined with the 2nd Fermi/GBM catalog. The results from the two instruments are fully consistent. We find that 78% of long GRBs and 85% of short GRBs cannot be explained by standard slow cooling synchrotron from a Maxwellian distribution of electrons, and almost half the spectra are more narrow that monoenergetic synchrotron. Conversely, photospheric emission can explain the spectra if mechanisms are invoked to give a spectrum much broader than a blackbody. We further find that the median widths of spectra from long and short GRBs are significantly different, and this is thus a new, independent distinction between the two classes. We will discuss the implications of theseresults and the constraints they place on possible emission mechanisms.

Speaker: Magnus Axelsson

axelsson_texas2015_grb.key

axelsson_texas2015_grb.pdf

17:55 Study of GRB light curve decay indices in the afterglow phase

In this work we study the distribution of temporal power-law decay indices, $\alpha$, in the Gamma Ray Burst (GRB) afterglow phase, fitted for a sample of $164$ long GRBs with known redshifts using a power-law form. These indices are compared to the values of characteristic afterglow luminosity, $L_a$, the time, $T_a^*$, and the analogous decay index, $\alpha_W$, derived with global light curve fitting using the Willingale et al. (2007) model. This model fitting yields similar distributions of $\alpha_W$ to the fitted $\alpha$, but for several bursts difference between these indices can be significant. Analysis of the ($\alpha$, $L_a$) distribution reveals a weak correlation of these quantities. However, we discovered a significant regular trend when studying distribution of GRB $\alpha$ values at the $L_a$, vs. $T_a^*$ (LT) plane, with a differences of the $\alpha$ parameters below and above the fitted LT correlation line (Dainotti et al. 2008). Study of the presented systematic trend may allow one for constraining the physical models for GRBs. A proposed toy model accounting for this systematics applied to the analyzed GRB distribution results in increasing the LT correlation coefficient.

Speaker: Mrs Roberta Del Vecchio (Astronomical Observatory of the Jagiellonian University)

posterGinevra1.pdf

posterginevra_Talk.pdf

17:58 Observed properties of high redshift Gamma-Ray Bursts

I shall compare the observed properties of high redshift long Gamma-Ray Bursts with those at lower redshifts

Speaker: Graziella Pizzichini (INAF)

13_1758_Pizzichini_Observed_properties_of_high_redshift_Gamma-Ray_Bursts.pdf

13_1758_Pizzichini_Observed_properties_of_high_redshift_Gamma-Ray_Bursts_POSTER.ppt

18:01 Moving observed Short GRBs both off-axis and into the local Universe

Short Gamma Ray Bursts (SGRBs) are among the best source candidates of simultaneous electromagnetic radiation and gravitational waves (GWs) in the frequency range covered by the imminent second generation laser interferometer detectors Advanced LIGO and Advanced Virgo. SGRB afterglow properties in the electromagnetic spectrum (e.g. photon flux intensity, variability time scale) can be very different one with the other, and the statistics available so far may provide average properties not representative of the population. In this work we compute the expected afterglow emission of a sample of short GRBs as they were within the GW detector horizons, and if they were detected from line of sights out of the jet cone (i.e. off-axis), that for geometrical reasons is a more likely configuration. We discuss our results in the context of the observational strategies to simultanously detect these sources both in GW and electromagnetic radiations with present and future facilities.

Speakers: Dr Giovanni De Cesare (IASF-Bologna), Giulia Stratta (Urbino University), Dr Giuseppe Greco (Urbino University), Dr Marica Branchesi (Urbino University)

13_1801_Stratta_Moving_Observed_Short_GRBs.pdf

18:04 gap

16:15 → 18:45 15 - Binaries: HXMXB

Convener: Alessandro Papitto

16:15 Swift and the Supergiant Fast X-ray Transient outburst factory

We present the results of the Swift Supergiant Fast X-ray Transients project, which has been exploiting *Swift*'s capabilities in a systematic study of SFXTs and classical supergiant X-ray binaries (SGXBs) since 2007. The unique combination of sensitivity and scheduling flexibility of *Swift*/XRT allowed us to perform an efficient long-term monitoring of 16 including both SFXTs and classical SGXBs. We followed source activity across more than 4 orders of magnitude in X-ray luminosity and sampled the light curves on timescales spanning from hours to years. Our measurements of dynamic ranges, duty cycles as a function of luminosity, and of luminosity distributions show systematic differences that help discriminate between different models of SFXTs/SGXBs, while our outburst follow-ups provide a steady advancement in the comprehension of the SFXT phenomenon. In particular, the observations of the SFXT prototype IGR J17544-2619 on 2014 October 10, when the source reached a peak luminosity of $3\times10^{38}$ erg s$^{-1}$, challenged, for the first time, the maximum theoretical luminosity achievable by a wind-fed neutron star high mass X-ray binary. We propose that this giant outburst was due to the formation of a transient accretion disc around the compact object.

Speaker: Patrizia Romano (INAF)

Homepage: The Swift SFXT Project

romanop_sfxts_texas15_pub.pdf

16:40 High-mass X-ray binary systems through the eyes of INTEGRAL

Review of the most prominent results obtained with the INTEGRAL observatory for high-mass X-ray binary systems (HMXBs) is presented. Hard X-ray observations by INTEGRAL have broadened significantly our knowledge about X-ray binaries in the Milky Way. During dozen years the observatory discovered new types and populations of binary systems, like supergiant fast x-ray transients, heavily obscured sources, has permitted the studies of cyclotron resonance scattering features with the high resolution for several persistent and transient pulsars. The unique characteristics of INTEGRAL in a combination with its long life time as well as deep observations of the Galactic plane played a fundamental role for building a complete catalogue of HXMBs, to study the different populations of these systems in our Galaxy, to measure their spatial distribution and luminosity function and to constrain some of the time scales and processes driving their birth and evolution.

Speaker: Alexander Lutovinov (Space Research Institute)

15_1640_Lutovinov_talk_texas2015.pdf

15_1640_Lutovinov_talk_texas2015.ppt

17:05 Vela X-1 and sgHMXB: hydro driven hard X-rays

The dynamic of the accretion of stellar wind on the pulsar in Vela X-1 is dominated by unstable hydrodynamical flows. INTEGRAL discovered off-states, 10³⁷ erg/s flares, quasi- periodic oscillations and log normal flux distribution, which can all be reproduced by hydrodynamical simulations, revealing the complex motion of the bow shocks moving either towards or away from the neutron star. With the help of hydrodynamic simulations and hard X-ray observations can also be used to probe the scattering of hard X-ray photons on the stellar wind to determine the velocity and density profile of the wind very close to the surface of the supergiant companion. This provides a unique measurement of the early acceleration of stellar winds in massive stars, otherwise poorly constrained.

Speaker: Antonis Manousakis

15_1705_Manousakis_VelaX1_and_sgHMXB.pdf

17:25 Correlation study of spectral parameters of NS-HMXBs with Suzaku

We present a broadband spectral analysis of classical HMXBs (supergiant and Be/X-ray binaries) and Supergiant Fast X-ray Transients (SFXTs) using data from XIS and PIN instruments onboard Suzaku. After fitting the X-ray spectra of 36 sources with a single model: a powerlaw and a high energy cutoff (where required), we studied the correlation between various spectral parameters. We present the following results: (i) We find a linear correlation between the cyclotron line energy and the cutoff energy as is previously reported in literature using RXTE and Ginga data (for cyclotron line energy less than 35 keV). Using Suzaku obervations, though, we find that there is more than one slope of variation between the two quantities. (ii) The variation of cutoff energy with luminosity indicate that NS-HMXBs seem to be divided into two classes following two different trends. This division is not on the basis of different beaming mechanism, as can be studied from the pattern of their pulse profiles. These two groups, notably, show two different patterns when the variation of their photonindex is studied against their cutoff energies. (iii) As seen for LMXBs, we note an anticorrelation between the spectral index and luminosity. (iv) Unlike previous works, we do not see anticorrelation between the X-ray luminosity and the equivalent width of Kα lines (Baldwin effect). (vi) The equivalent width and the iron Kα line flux is smaller in SFXTs than in classical NS-HMXBs.

Speaker: Ms Pragati Pradhan (St. Joseph's College, Darjeeling, India & North Bengal University, Siliguri, India)

texas1.pdf

17:45 Orbital resolved spectroscopy of GX 301-2 with MAXI

GX 301-2, a bright high-mass X-ray binary with an orbital period of 41.5 days, exhibits stable periodic orbital intensity modulations with a strong pre-periastron X-ray flare. Several models have been proposed to explain the accretion at different orbital phases, invoking accretion via stellar wind, equatorial disc, and accretion stream from the companion star. We present results from exhaustive orbital phase resolved spectroscopic measurements of GX 301-2 using data from the Gas Slit Camera onboard MAXI. Using spectroscopic analysis of the MAXI data with unprecedented orbital coverage for many orbits continuously, we have found a strong orbital dependence of the absorption column density and equivalent width of the iron emission line. A very large equivalent width of the iron line along with a small value of the column density in the orbital phase range 0.10–0.30 after the periastron passage indicates the presence of high density absorbing matter behind the neutron star in this orbital phase range. A low energy excess is also found in the spectrum at orbital phases around the pre-periastron X-ray flare. The orbital dependence of these parameters are then used to examine the various models about mode of accretion on to the neutron star in GX 301-2.

Speaker: Ms Nazma Islam (Indian Institute of Science, Raman Research Institute, Bangalore, India)

texas_talk_IslamN.pdf

18:05 Broadband study of X-Per using Suzaku observations

We present detailed broadband timing and spectral analysis of the persistent, low luminosity and slowly spinning pulsar 'X-per' using a Suzaku observation of the source. The spectrum is unusually hard with pulsations detected up to 70 keV. The spectrum also hosts several interesting features like evidence of a cyclotron line at 30 keV, and presence of a soft-excess below 2 keV. Considering these, the broadband Suzaku observation is ideal to study the energy dependence of the pulse profiles, and critically compare the different spectral models of accretion powered pulsars applicable to the source. The hardness ratio varies by more than a factor of two during the duration of the observation, and the change in spectral parameters are mapped by performing time resolved spectroscopy. The results are compared with other persistent Be accreting systems.

Speaker: Chandreyee Maitra (CEA Saclay)

proc_cmaitra_x-per.pdf

X-per_texas_cmaitra.pdf

18:20 Orbital evolution and search for eccentricity and apsidal motion in the eclipsing HMXB 4U 1700–37

In the absence of detectable pulsations in the eclipsing High Mass X-ray binary 4U 1700–37, the orbital period decay is necessarily determined from the eclipse timing measurements. We have used the earlier reported mid-eclipse time measurements of 4U 1700–37 together with new measurements from long term light curves obtained with the all sky monitors RXTE–ASM, Swift–BAT and MAXI–GSC, as well as observations with RXTE–PCA, to measure the long term orbital evolution of this binary. The orbital period decay rate of the system is estimated to be 'P/P = −(4.7 ± 1.9) × 10^{−7} yr^{−1} , smaller compared to its previous estimates. We have also used the mid-eclipse times and the eclipse duration measurements obtained from 10 years long X-ray light curve obtained with Swift–BAT to separately put constraints on the eccentricity of the binary system and attempted to measure any apsidal motion. For a reasonable rate of apsidal motion for this binary system, the eccentricity is found to be less than 0.008, which limits our ability to determine the apsidal motion rate from the current data. We discuss the discrepancy of the current limit of eccentricity with the earlier reported values from radial velocity measurements of the companion star.

Speaker: Ms Nazma Islam (Indian Institute of Science, Raman Research Institute, India)

poster_IslamN.pdf

teaser_poster_IslamN.pdf

18:24 Blowing in the wind : accretion in high mass X-ray binaries

Compact objects in high mass X-ray binaries (HMXB), where the companion star underfills its Roche lobe, have been spotted as X-ray emitters, probably due to the presence of a surrounding disc, along with their low mass counterparts (LMXB). However, if the disc formation is well understood in LMXB where matter is poured through the first Lagrangian point, things get messier in HMXB, especially in Supergiant-HMXB whose number has almost tripled thanks to recent observations with Integral (Chaty 2011, Walter et al 2015). Indeed, the massive companion stars have dense and fast winds which can lead to a Bondi-Hoyle like accretion (a.k.a. wind accretion) onto the compact body. Given the variability of the instantaneous mass and angular momentum accretion rates in this configuration, the disc formation is way more uncertain. The observed photometric and spectral variabilities of the flux might reflect transient accretion phases due to orbital scale modulations like a clumpy wind or non-homogeneous streamlines.

So as to get a better feel of the properties of the subsequently formed disc, we designed a numerical setup able to grasp the huge spatial dynamics of the Bondi-Hoyle accretion onto a compact object for non-relativistic wind velocities (El Mellah and Casse, 2015). From the accretion radius of the black hole down to the vicinity of its event horizon, the flow spans up to 5 orders-of-magnitude. Taking the most of the highly parallelized code MPI-AMRVAC, we characterized the flow properties in the axysymmetric configuration, both in terms of observable-related quantities (e.g. mass accretion rates as a function of the Mach number of the unperturbed flow) and in terms of topology of the sonic surface, confirming the result derived in Foglizzo and Ruffert (1996). We then introduced non axysymmetric effects for specific sets of orbital parameters in full 3D simulations and monitored the formation and permanence of a disc-like structure.

Speaker: Ileyk EL MELLAH (Paris 7 Diderot - APC laboratory)

elmellah_poster.pdf

elmellah_teaser.pdf

Personal webpage

18:27 gap

16:15 → 18:45 08 - Cosmic microwave background

Convener: Antony Lewis (University of Sussex)

16:15 Dark matter decay and cosmic reionization

We study the impact of dark matter decay on cosmic reionization. We derive new constraints on the dark matter decay rate by using the newest CMB observations, assuming two different parametrizations of standard reionization.

Speaker: Ms Isabel Oldengott (Universität Bielefeld)

TexasSymposium_2015.pdf

16:35 Is there evidence for anisotropy in CMB data?

Large scales in the Cosmic Microwave Background (CMB) may break statistical isotropy. Bianchi models are often invoked as a possible explanation for these low-\ell features: they provide an anisotropic underlying pattern over which the usual stochastic fluctuations are superimposed. However, the Bianchi models generally employed in the analysis of CMB data — despite mimicking the anomalies in the CMB temperature map — overproduce B-mode polarisation due to the very specific way in which they break isotropy. In this work, we consider the most general way to break Friedmann-Robertson-Walker isotropy that still preserves homogeneity and test for its signatures in Planck temperature and polarisation map; WMAP data are also analysed for comparison. In addition to the well-known Bianchi models that are more commonly employed in the literature, we consider more physical and untested-for Bianchi models that comply with polarisation constraints. We also show that improved constraints on anisotropy may be obtained by extending the likelihood to high \ell. Nested sampling techniques are employed to determine whether the Bayesian evidence favours anisotropic universes over the standard Lambda-CDM scenario.

Speaker: Ms Daniela Saadeh (University College London)

08_1635_Saadeh_Is there evidence for anisotropy.pdf

08_1635_Saadeh_Is there evidence for anisotropy.pptx

16:55 Current constraints and forecasts on the tilt and running of the primordial tensor spectrum

Gravitational waves can be produced by a wide range of astrophysical phenomena, such as inspiral and merging of neutron stars and black holes, supernova of massive stars, accreting neutron stars, etc. This talk is focused, instead, on a stochastic background of gravitational waves (GWs) of cosmological origin, like the one predicted by inflation. I start by considering a power law parametrization of the frequency spectrum of primordial tensor modes, with tilt $n_T$ and tensor-to-scalar ratio $r$. I discuss the constraints that can be placed on these parameters by Cosmic Microwave Background (CMB) temperature and polarization anisotropies alone, and then show how such constraints become stronger if one takes into account the contribution of gravitational waves to the radiation energy density. GWs add to the effective number of relativistic degrees of freedom $N_\text{eff} = 3.046 + N_\text{eff}^\text{GW}$, and then have an effect on the CMB angular spectra and the primordial abundances. More precisely, we find that the $95\%$ CL limits on the tilt $n_T$ at a pivot scale of $0.01\,\text{Mpc}^{-1}$ go from $n_T = 1.7^{+2.1}_{-2.0}$ (Planck + BKP dataset, no $N_\text{eff}^\text{GW}$) to $n_T = 0.06^{+0.78}_{-0.56}$ (with $N_\text{eff}^\text{GW}$). In the second part of the talk I discuss the forecasts on a spectrum described by a spectral index $n_T$ and its running $n_{T,\text{run}}$: our analysis considers a future COrE-like satellite mission combined with direct-detection experiments like AdvLIGO. When the contribution of primordial tensor modes to CMB spectral distortions of the $\mu$-type is taken into account, we add the future measurements of the CMB spectrum by a PIXIE-like experiment. For these forecasts two fiducial cosmologies are considered: at first a cosmology with no primordial gravitational waves, in order to see how well future experiments will be able to measure the tensor parameters. The second forecast takes as fiducial model one where the tensor-to-scalar ratio is of order $10^{-2}$ (a value that can be reached by futuristic ground-based experiments such as AdvACT), and the tilt and running are fixed by the consistency relations of single-field slow-roll inflation. In the final part of the talk, I discuss the implications of our results for models of single-field slow-roll inflation.

Speaker: Mr Giovanni Cabass (Physics Department and INFN, “La Sapienza” University of Rome)

slides-geneva-png.pdf

17:15 Cosmological constraints on the neutron lifetime

We show how to derive new constraints on the neutron lifetime based on cosmological observations. Under the assumption of standard Big Bang Nucleosynthesis, the abundance of light elements, in particular Helium, is strongly dependent on the neutron lifetime. From CMB anisotropies it is possible to constrain primordial abundances of light elements, inferring the value of the neutron lifetime. We start considering recent Planck 2015 results of temperature and polarization anisotropies of the CMB. We show how including direct astrophysical measurements of primordial Helium abundance it is possible to obtain stringent constraints on the neutron lifetime. Furthermore, we compute the neutron lifetime theoretical expectation and we compare this value with our results, with the value quoted by the Particle Data Group and with the ones obtained in ``bottle method" and ``beam method" experiments. Finally, we perform forecasts on different future CMB experiments. We highlight the high precision that can be reach from these experiments, such as CMB surveys as COrE+, in combination with a weak lensing survey as EUCLID, that could constrain the neutron lifetime up to a $\sim 6$ s precision.

Speaker: Laura Salvati (University of Rome, Sapienza)

08_1715_LauraSalvati_Cosmological constraints on the neutron lifetime.pdf

17:35 UV sensitivity of Higgs inflation

The idea of introducing a non minimal coupling between the Higgs boson and the gravity sector gives successful predictions for inflation without needing new particles beyond the ones we know. Quantum mechanically the model is only consistent until the unitarity cutoff. Possible UV completions beyond this cutoff could change its predictions. If this is the case it means that we would lose the minimalist approach that inspires the model. Treating Higgs inflation in the context of effective field theories we consider the effect of threshold corrections on the renormalization group flow. We show that the CMB predictions are protected from this type of UV corrections.

Speaker: Mr Jacopo Fumagalli (Nikhef)

08_1735_Fumagalli_UV insensitivity of Higgs Inflation.pdf

08_1735_Fumagalli_UV insensitivity of Higgs Inflation.pptx

17:55 gap

16:15 → 18:45 06 - Early universe

Convener: Daniel G. Figueroa (CERN)

16:15 On stability of electroweak vacuum during inflation

We study Coleman – De Luccia tunneling of the Standard Model Higgs field during inflation in the case when the electroweak vacuum is metastable. We verify that the tunneling rate is exponentially suppressed. The main contribution to the suppression is the same as in flat space-time. We analytically estimate the corrections due to the expansion of the universe and an effective mass term in the Higgs potential that can be present at inflation.

Speaker: Andrey Shkerin (EPFL)

Texas2015.pdf

16:35 A stiff Higgstory of the Universe

I will present the cosmological implications of the decay of the Standard Model Higgs after Inflation, when assuming a post-inflationary/pre-BBN expansion history driven by a stiff source with equation of state w > 1/3. In particular, I will discuss first the realisation of a successful 'reheating' mechanism, and secondly, the production of a large background of gravitational waves by the Higgs decay products.

Speaker: Dr Daniel G. Figueroa (CERN)

DaniFigueroaCERN_TexasSymp2015.pdf

16:55 Parametric resonance after hilltop inflation caused by an inhomogeneous inflaton field

I will first give a short overview of preheating after hilltop inflation. In the main part of the talk I will discuss how the dynamics can change when the inflaton couples to another scalar field, e.g. a right-handed sneutrino, which provides a mechanism for generating the correct initial conditions for inflation and also a decay channel for the inflaton that allows for non-thermal leptogenesis. I will particularly discuss how the known phases of preheating during which the inflaton field becomes fully inhomogeneous, can be followed by a subsequent preheating phase where the fluctuations of the secondary field gets resonantly enhanced, from initially tiny amplitudes up to amplitudes of the same order (and even larger) as the ones of the inflaton field. This resonant enhancement differs from the usual parametric resonance as the inflaton field is highly inhomogenous at the time the enhancement takes place.

Speaker: Francesco Cefalà (University of Basel)

TEXAS_acrobat.pdf

17:15 Preheating after hilltop inflation

During hilltop inflation, the inflaton rolls away from the maximum of its potential and towards the minimum where the universe reheats. The first stage of reheating, preheating, is non-perturbative and, in this model, localized oscillating bubbles of the inflaton field, called oscillons, are formed. Furthermore, when other fields are present, they can be produced via a parametric resonance with the non-homogeneous inflaton field. In this talk, I will discuss lattice simulations of the evolution of oscillons, how they are affected by the resonance with another field and their effect on the expansion history of the universe.

Speaker: Stefano Orani (Basel University)

Orani.pdf

17:35 The Cosmic Laboratory: Probing Inflation with Galaxy Clustering

The large-scale distribution of galaxies is a powerful probe of the physics of Inflation. In this talk, I will explain what it would take for a future galaxy survey to use galaxies as a probe of primordial non-Gaussianity in order to distinguish between single-field and multi-field Inflation, and I will introduce a specific proposal for such a survey, called SPHEREx. I will also revisit the prediction for the exact level of non-Gaussianity and scale-dependent bias in single-field Inflation.

Speaker: Roland de Putter

17:55 The Effective Strength of Gravity and the scale of Inflation

At any given energy, gravitational interactions have a strength set by a characteristic scale $M_*$, inferred from amplitudes calculated in an effective theory with a strong coupling scale $M_{**}$. These are in general different from each other and $M_{\rm pl}$, the macroscopic strength of gravity as determined by (laboratory scale) Cavendish experiments. We explore several consequences of this fact for inflationary cosmology and CMB observables.

Speaker: Subodh Patil

texas.pdf

18:15 Implications of the primordial power asymmetry for inflation

It is both remarkable, and disappointing, that only two parameters describing the primordial perturbations can explain the statistical properties of millions of CMB temperature perturbations. However, the persistence of several large-scale cosmological anomalies in WMAP and Planck satellite data may provide a clue to new physics. I will discuss how inflationary models can explain the observed dipolar power asymmetry, and the extreme difficulties of building a complete working model.

Speaker: Christian Byrnes (University of Sussex (GB))

06_1815_Byrnes-asymmetry.key

06_1815_Byrnes-asymmetry.pdf

18:35 gap

16:15 → 18:45 02 - Exact solutions

Convener: Mustapha Ishak (The University of Texas at Dallas)

16:15 First-order cosmological perturbations engendered by point-like masses: all scales covered

In the framework of the concordance cosmological model the first-order scalar and vector perturbations of the homogeneous background are derived without any supplementary approximations in addition to the weak gravitational field limit. The sources of these perturbations (inhomogeneities) are presented in the discrete form of a system of separate point-like gravitating masses. The obtained expressions for the metric corrections are valid at all (sub-horizon and super-horizon) scales and converge in all points except the locations of the sources, and their average values are zero (thus, first-order backreaction effects are absent). Both the Minkowski background limit and the Newtonian cosmological approximation are reached under certain well-defined conditions. An important feature of the velocity-independent part of the scalar perturbation is revealed: up to an additive constant it represents a sum of Yukawa potentials produced by inhomogeneities with the same finite time-dependent Yukawa interaction range. The suggesting itself connection between this range and the homogeneity scale is briefly discussed along with other possible physical implications.

Speaker: Maxim Eingorn

arXiv:1509.03835v1

Eingorn_Geneva_2015.pdf

16:35 On homogeneous and isotropic universe

We give a simple example of space-time metric, illustrating that homogeneity and isotropy of space slices at all moments of time is not obligatory lifted to a full system of six Killing vector fields in space-time, thus it cannot be interpreted as a symmetry of a four dimensional metric. The metric depends on two arbitrary and independent functions of time. One of these functions is the usual scale factor. The second function cannot be removed by coordinate transformations. We prove that it must be equal to zero, if the metric satisfies Einstein's equations and the matter energy momentum tensor is homogeneous and isotropic. A new, equivalent, definition of homogeneous and isotropic space-time is given.

Speaker: Mikhail Katanaev (Steklov Mathematical Institute, Moscow)

02_1635_MikhailKatanaev_Homogeneous isotropic universe.pdf

16:55 Covariant Perturbations of the Scalar-Tensor Schwarzschild Black Hole

In this talk I will review recent results regarding covariant, gauge-invariant perturbations to the scalar-tensor Schwarzschild black hole in the 1+1+2 formalism. I will discuss how we can introduce a set of master functions based on the Weyl tensor in order to cleanly decouple the evolution of tensor modes from the scalar modes. Relations to 2+2 and Newman-Penrose formalism will be briefly discussed.

Speaker: Geraint Pratten (University of Sussex)

02_1700_Geraint_Pratten_CovariantperturbationoftheSTSchwBlackHole.pdf

17:15 Confronting anisotropic cosmological models with real-time cosmology

A repetition of the same high-resolution and large-volume observation, after ten or more years, gives access to the fourth dimension in observational cosmology, perpendicular to the light-cone. I discuss how various toy models can be distinguished by decomposing the long-time-difference maps into multipole vectors. A next-generation GAIA-like satellite with ten times GAIA's resolution, should be able to distinguish rotation from anisotropic expansion.

Speaker: Wessel Valkenburg (Leiden University)

wvAtTexasGeneva_InhCos.key

wvAtTexasGeneva_InhCos.pdf

17:35 High-precision cosmology and inhomogeneities: exact results in the geodesic light-cone gauge

The remarkable properties of the recently proposed geodesic light-cone (GLC) gauge allow to get some new interesting results to face the problem of inhomogeneities and their backreaction. Indeed, GLC simply consists of gauge fixing the metric tensor on the past light-cone of the observer. Thanks to this choice, several interesting physical observables, related to photons, can be evaluated within this framework. In this talk, we will present an overview on these recent results: in particular, we will show how the geodesic deviation equation can be exactly solved, giving an exact expression for the so called Jacobi map. Furthermore, its link with cosmological distances and weak gravitational lensing will be discussed.

Speaker: Giuseppe Fanizza (Università degli Studi di Bari "Aldo Moro")

Fanizza_Texas_2015.pdf

17:55 Discussion session on averaging and backreaction in cosmology

16:15 → 18:45 18 - Gal. accel. & pulsars: Galactic accelerators

Convener: Marco Tavani (INAF)

16:15 Pulsar observations with the MAGIC telescopes

Although more than 150 gamma-ray pulsars are known in GeV band, their spectra roll off above 10 GeV and only two pulsars are detected at about 50 GeV, namely Crab and Vela. There is also a large difference between Crab and Vela. Crab spectrum is extending above 1 TeV, while Vela has a very soft spectrum, becoming almost undetectable at 100 GeV. In order to further understand the emission mechanism of pulsars, it is necessary to continue search pulsars above 50 GeV with imaging atmospheric Cherenkov telescopes. In this talk, we will report on the recent observations of Crab and Geminga pulsars by the MAGIC telescopes, along with the analysis results of Fermi-LAT data. The future prospect on the gamma-ray observation with MAGIC will also be shown.

Speaker: Dr Takayuki Saito (Kyoto University)

PulsarWithMAGICTSaitoV3.pdf

16:35 The intriguing double torus-jet PWN around PSR J0855-4644

PSR J0855-4644 is a nearby, fast spinning, and energetic radio pulsar spatially coincident with the rim of the supernova remnant RX J0852.0-4622 (aka Vela Jr). XMM Newton observations of the pulsar region have shown an arcmin scale extended emission, the pulsar wind nebula (PWN), around the X-ray counterpart of the pulsar. Here, we present results from the small scale structure of the nebula provided by a Chandra observation of this source. This observation has revealed an arc second scale compact PWN around the pulsar showing a possible double 'torus+jet' morphology. This makes it only the third source of its kind, and being an nearby object provides us with the golden opportunity to investigate the physics of equatorial and polar outflows in PWNe. Modeling the geometry of this source is also crucial to understand why no gamma-ray pulsations have been detected by the Fermi-LAT telescope for this high E_dot/d^2 pulsar. In order to constrain the pulsar spin inclination angle, we model the double torus morphology and then compare it with theoretical phase-plots to understand this radio loud, gamma-ray quiet system.

Speaker: Chandreyee Maitra (CEA Saclay)

psr-0855-texas-cmaitra.pdf

16:55 A Pulsar Wind Nebula Origin for Luminous TeV Source HESS J1640-465

TeV gamma-rays indicate the presence of extremely high-energy particles. While many discrete TeV sources have been identified in the Galactic plane, the origin of these particles is often unclear. This is especially true for HESS J1640-465, among the most luminous TeV sources in the Milky Way, which is coincident with both a radio supernova remnant and an energetic X-ray pulsar and pulsar wind nebula (PWN). In this talk, I will present the results of a recent *Chandra* observation of this source, which indicates the PWN is considerably larger and more X-ray luminous than previously thought, and fit to its broadband spectral energy diagram assuming a PWN origin for the observed X-ray and gamma-ray emission, which constrains both the spectrum of particles accelerated in this source and the birth properties of the central neutron star. These results are important for determining both the origin of the gamma-rays detected from this source, and how the production of the highest energy leptons in the galaxy.

Speaker: Joseph D Gelfand

18_1655_GELFAND_a_pulsar_wind_nebula_origin_for_luminous_tev_source_hess_j1640-465.pdf

18_1655_GELFAND_a_pulsar_wind_nebula_origin_for_luminous_tev_source_hess_j1640-465.pptx

17:15 First-order Fermi acceleration at pulsar wind termination shock.

The Pulsar Wind Nebulae (PWNe) PSR B1259-63 has been observed to emit periodic GeV flares, whose power can be comparable to the total pulsar spin-down luminosity. Because of the short timescale involved, these photons are likely to be produced via inverse Compton scattering of stellar photons or Synchrotron radiation by a population of very energetic electrons (from GeV to TeV energies) in proximity of the wind termination shock (TS). This perpendicular shock is created by the interaction between the magnetised, relativistic, electron-positron wind launched by the pulsar with the companion star outflow. When the rotational frequency of the pulsar is greater than the local plasma frequency in the wind, a shock precursor forms ahead of the TS, where the Poynting flux is dissipated. This condition is satisfied at the TS in a gamma-ray binary when the system is far from periastron, but not necessarily when the stars are in close proximity to each other (Mochol & Kirk 2013). It is stll unclear whether and how this structure can accelerate electrons to high energies. We investigate this in a two-step procedure. Firstly, a 1-dimensional, relativistic, 2-fluid code is used to reproduce the turbulent fields in the equatorial plane at the location of the TS. We numerically integrate test particle trajectories in the background fields of a steady configuration of the precursor realised for an upstream Lorentz factor $\Gamma=40$ and a magnetisation parameter $\sigma=10$. We follow each particle until it either escapes downstream after transmission or upstream after reflection. We find that $\sim 50\%$ of the incoming particles are reflected upstream by the turbulent fields for these parameters. Secondly, we simulate Fermi-like acceleration by supplementing magnetic fluctuations with prescribed statistical properties both in the pulsar wind upstream of the shock, and in the nebula downstream of the shock, where the field is assumed to have been dissipated. The resulting stochastic trajectories are numerically integrated (Achterberg & Kruells 1992). We compare the power-law index and the angular distribution of accelerated particles with the same quantities obtained with a numerical simulation where the average magnetic field is null on both sides of the shock and the only source of deflection for energetic particles is the scattering off magnetic irregularities (Achterberg et al. 2001). We argue that the proposed scenario is relevant for PWNe in $\gamma$-ray binaries such as PSR B1259-63.

Speaker: Mr Simone Giacche` (Max-Planck Institute for Nuclear Physics)

18_1715_Giacche_First order Fermi acceleration.pdf

17:35 Rapid particle acceleration at perpendicular shocks

Perpendicular shocks are shown to be rapid astrophysical particle accelerators. They perform optimally when the ratio of the shock speed to the particle speed roughly equals the ratio of the scattering rate to the gyro frequency. Analytical methods and Monte-Carlo simulations are used to solve the kinetic equation that govern the anisotropy generated at these shocks, finding a softer spectral index than the standard result of diffusive shock acceleration, and an acceleration time significantly shorter than the frequently quoted "Bohm limit". Amongst other implications, these results provide a theoretical basis for the thirty-year-old conjecture that a supernova exploding into the wind of a Wolf-Rayet star may accelerate protons to an energy exceeding $10^{15}\,$eV.

Speaker: John Kirk

18_1735_John Kirk_ Rapid particle acceleration.pdf

17:55 Kinetic simulations of relativistic harmonic magnetic equilibria

We will present the results of kinetic particle-in-cell numerical simulations of relativistic harmonic magnetic equilibria, so called "ABC fields". These equilibria have been recently shown by relativistic magnetofluid simulations to be generally unstable. An ideal plasma instability leads to the formation of dynamical current layers where magnetic energy is dissipated via reconnection and particles are accelerated efficiently. This concept may provide a viable generic scenario for the production of rapid gamma-ray and X-ray flares in strongly magnetized astrophysical environments, such as relativistic jets of active galaxies, gamma-ray bursts, pulsar wind nebulae (Crab), or the Galactic Center source Sgr A*.

Speaker: Dr Krzysztof Nalewajko (Stanford University)

nalewajko_texas15.pdf

18:15 Multipolar electromagnetic fields around neutron stars: exact vacuum solutions and related properties.

The magnetic field topology in the surrounding of neutron stars is one of the key questions in pulsar magnetospheric physics. A very extensive literature exists about the assumption of a dipolar magnetic field but very little progress has been made in attempts to include multipolar components in a self-consistent way. In this talk, we study the effect of multipolar electromagnetic fields anchored in the star. We give exact analytical solutions in closed form for any order~l and apply them to the retarded point quadrupole~(l=2), hexapole~(l=3) and octopole~(l=4), a generalization of the retarded point dipole~(l=1). We also compare the Poynting flux from each multipole and show that the spin down luminosity depends on the ratio R/rL, R being the neutron star radius and rL the light-cylinder radius. Therefore the braking index also depends on R/rL. As such multipole fields possess very different topology, most importantly smaller length scales compared to the dipolar field, especially close to the neutron star, we investigate the deformation of the polar cap induced by these multipolar fields. Such fields could have a strong impact on the interpretation of the pulsed radio emission suspected to emanate from these polar caps as well as on the inferred geometry deduced from the high-energy light-curve fitting. Discrepancies between the two-pole caustic model and our new multipole-caustic model are emphasized with the quadrupole field. To this respect, we demonstrate that working with only a dipole field can be very misleading.

Speaker: Jérôme Pétri (Université de Strasbourg)

18_1815_Petri_Multipolar_ Electromagnetic_Fields.pdf

18:18 gap

16:15 → 18:45 07 - Large scale structures

Convener: Vincent Desjacques

16:15 Cosmological nonlinear density and velocity power spectra

We present the leading order nonlinear density and velocity power spectra including the vector- and tensor-type perturbation simultaneously excited by the scalar-type perturbation in nonlinear order. Concerning density and velocity perturbations of the pressureless matter in perturbation regime well inside of matter-dominated epoch, we show that pure Einstein’s gravity contributions appearing from the third order are entirely negligible in all scales.

Speaker: Prof. Jai-chan Hwang (Kyunpook National Univ.)

07_1615_Hwang_Cosmological Nonlinear density and velocity.pdf

07_1615_Hwang_Cosmological Nonlinear density and velocity.pptx

16:35 General Relativity and Cosmic Structure Formation

The Newtonian approximation which is usually invoked in N-body simulations of cosmic large scale structure relies on the assumptions that gravitational fields are weak and that they are only sourced by nonrelativistic matter. The latter constitutes an implicit assumption about the nature of the "dark" components of the Universe (dark matter and dark energy), thereby precluding a serious assessment of some potentially interesting models. Here we present the first N-body simulations of cosmic structure formation based on a weak field approximation to General Relativity, taking into account all six degrees of freedom of the metric. The geodesic equations are solved consistently also for relativistic particles, such as massive neutrinos. Our approach is very general and can be applied to various settings where the Newtonian approximation would be unreliable or inconsistent, for instance some models of dynamical dark energy or modified gravity.

Speaker: Julian Adamek (Université de Genève)

07_Adamek_General Relativity and Cosmic Structure Formation.pdf

16:55 Large Scale Structure with interacting Vacuum: the non-linear regime in the post-Friedman approximation

General-relativistic cosmological models where vacuum interacts with cold dark matter (iV-CDM models) maybe a good alternative to the standard LCDM scenario. The post-Friedmann approximation generalises to cosmology post-Newtonian methods and we have used it to extract frame-dragging, a pure GR effect, from standard N-body simulations in LCDM and in f(R) models. After briefly summarising the iVCDM scenario and the post-Friedmann approximation I will discuss its extension from LCDM to the iVCDM case, concluding with an outlook on future work.

Speaker: Marco Bruni (University of Portsmouth)

07_1655_Bruni_LSS _with_interacting_vacuum.key

07_1655_Bruni_LSS__with_interacting_vacuum.pdf

17:15 One-dimensional models of cosmological perturbations: direct integration in the Fourier space

We propose a numerical approach to study the inhomogeneity growth in the Universe filled with a pressureless matter. The hydrodynamical equations for perturbations of the isotropic uniform cosmological background (non-relativistic stage) in the comoving frame are treated taking into account all nonlinear terms. The periodic boundary conditions are imposed. The problem is reduced to ordinary differential equations for an infinite chain of Fourier coefficients for hydrodynamical variables. We perform a numerical integration of these equations for randomly generated initial conditions (with proper truncation of the coefficients). This procedure is repeated for a number of representations of the ensemble of initial conditions to obtain a power spectrum of the density contrast. We test the method in two problems. (i) We derived an exact implicit solution which describes a one-dimensional collapse of plane gravitating shells. This is used to check the numerical solution for the Fourier coefficients and for the power spectrum. (ii) In case of the standard three-dimensional hydrodynamical equations but with one-dimensional (plane) initial conditions we proceed only numerically to derive first coefficients of the power spectrum. The results are used to study a nonlinear interaction of different Fourier modes. We estimate a realizability of this method as an alternative to the cosmological N-body simulations in case of a mildly non-linear situation.

Speaker: Vitalii Sliusar (Astronomical Observatory of Taras Shevchenko National University of Kyiv, Ukraine)

Sliusar-Zhdanov - Direct simulations_v2.ppt

Sliusar-Zhdanov - Direct simulations_v2.pptx

other

• 3d+1d+normal.gif
• 3d+1d+simple.gif
• Sliusar-Zhdanov - Direct simulations_v2.pdf

17:35 TSPT: Time-Sliced Perturbation Theory for Large Scale Structure

I will present a new perturbative approach to the description of cosmological structures in the mildly non-linear regime relevant at the distance scales from 10 to 100 Mpc. In this framework equal-time correlation functions of cosmological perturbations are calculated using an ensemble with time-dependent statistical weight. The scheme is free from unphysical infrared divergencies plaguing the traditional approaches and allows a systematic resummation of large infrared contributions to all orders of the perturbation theory. This greatly improves the description of the density power spectrum in the region of baryon acoustic oscillations. I will mention future directions, which include infrared resumption of higher-point correlation functions and renormalisation of the contributions coming from short-wavelength modes.

Speaker: Sergey Sibiryakov (CERN & EPFL & INR RAS)

07_1735_Sibiryakov_TSPT.pdf

17:55 Precision measurement of the local bias of dark matter halos

The large-scale local bias parameters of dark matter halos are essential to describe the statistics of halos and galaxies on large scales, as well as for the halo model of the matter distribution. We recently obtained precise measurements of the three leading bias parameters from simulations using a novel technique : the separate universe simulations. For b_2 and b_3, these are the most precise measurements to date. We compare our results with bias parameters obtained from two and three points cross-correlation functions and with theoretical predictions from the excursion set peaks (ESP) model. For b_1, we get agreement at percent level with the correlations measurements and at 5% level with the ESP. This plus the very good agreement also found for the other bias parameters confirms the validity of the method and its efficiency. In a separate project, we also report on new simulation results on the scale-dependent bias on primordial non-Gaussianity.

Speaker: Titouan Lazeyras (MPA)

07_1755_TitouanLazeyras_Precison measurements of local bias.pdf

18:15 Supercluster straightness as a cosmological test

We present how an anisotropic pattern of the cosmic web, which is vividly reflected in the filamentary structure of supercluster, changes if 1)the nature of dark energy differs from the cosmological constant or 2)the gravitational law deviates from the general theory of relativity with/without massive neutrinos. 1)The coupled dark energy (cDE) model where the coupling between dark energy and dark matter exists and 2)the f(R) gravity model which substitutes Ricci scalar R with function f(R) in the Einstein-Hilbert action with\without massive neutrinos are considered for the former and latter cases, respectively. Since the anisotropy of the clustering of galaxy clusters is represented in the degree of straightness of the supercluster, we calculate spine specific size of the supercluster as a measure of its straightness using the halo catalogs of N-body simulations for respective cosmologies at various epochs. It is found that both the cDE and f(R) gravity models have the effect of significantly bending the superclusters resulting in the smaller mean values of the spine specific sizes compared to that of the $\Lambda$CDM, whereas the massive neutrinos contribute to straightening the superclusters. Although the f(R) gravity with the massive neutrinos of the specific total neutrino mass is hard to discriminate from the $\Lambda$CDM since the effect of the f(R) gravity on the supercluster straightness is suppressed at the current epoch, its mean specific size deviates significantly from the value of the standard cosmology in higher redshifts (z$\ge$0.3). On the grounds that the difference in the degree of the supercluster straightness of cDE (f(R) gravity) from the $\Lambda$CDM increases (decreases) with redshift, the supercluster straightness should play a role of powerful cosmological test. A physical interpretation of our results as well as their cosmological implications are discussed.

Speaker: Mr Junsup Shim (Seoul National University)

18:18 gap

16:15 → 18:45 04 - Dark energy

Convener: Martin Kunz (Universite de Geneve (CH))

16:15 Using Atom Interferometry to Detect Chameleon Dark Energy

I will discuss the prospect that the first evidence for dark energy may be found through meter scale, laboratory based, atom interferometry experiments. I will discuss how, in order to be compatible with fifth force constraints, dark energy scalar fields must have a screening mechanism which hides their effects from us within the solar system. Focusing in particular on one such screening mechanism, known as the chameleon, where the field's mass becomes dependent on the environment I will show how the field behaves in the presence of a spherical source. In the presence of the kind of high vacuum associated with atom interferometry experiments, and when the test particle is an atom, it is possible to use the associated interference pattern to place constraints on the acceleration due to the fifth force of the chameleon field - this has already been used to rule out large regions of the chameleon parameter space and may one day be able to detect the force due to the dark energy field in the laboratory.

Speaker: Clare Burrage (University of Nottingham)

texas_geneva_2015.pdf

16:40 Causality in theories with more than one metric

I will discuss how considerations of causality put constraints on modifications of gravity where the perturbations in new degrees of freedom propagate on an acoustic metric different from the space time metric. More to come.

Speaker: Ignacy Leonard Sawicki (University of Geneva)

04_1640_Sawicki_Causality_in_theories_with_more_then_one_metric.pdf

17:05 Dark energy as a fixed point of the Einstein Yang-Mills Higgs Equations

We study the Einstein Yang-Mills Higgs equations in the SO(3) representation on a isotropic and homogeneous flat Universe, in the presence of radiation and matter fluids. We map the equations of motion into an autonomous dynamical system of first-order differential equations and we find the equilibrium points. We show that there is only one stable fixed point that corresponds to an accelerated expanding Universe in the future. In the past, instead, there is an unstable fixed point that implies a stiff-matter domination. In between, we find three other unstable fixed points, corresponding, in chronological order, to radiation domination, to matter domination, and, finally, to a transition from decelerated expansion to accelerated expansion. We solve the system numerically and we confirm that there are smooth trajectories that correctly describe the evolution of the Universe, from a remote past dominated by radiation to a remote future dominated by dark energy, passing through a matter-dominated phase.

Speaker: Massimiliano Rinaldi (University of Trento)

04_1705_Dark_Energy_as_a_fixed_point.pdf

17:29 Non-local gravity and comparison with observational datasets

We study the cosmological predictions of two recently proposed non-local modifications of General Relativity. Both models have the same number of parameters as $\Lambda$CDM, with a mass parameter $m$ replacing the cosmological constant. We implement the cosmological perturbations of the non-local models into a modification of the CLASS Boltzmann code, and we make a full comparison to CMB, BAO and supernova data. We find that the non-local models fit these datasets very well, at the same level as $\Lambda$CDM. For both non-local models parameter estimation using Planck+JLA+BAO data gives a value of $H_0$ slightly higher than in $\Lambda$CDM.

Speaker: Yves Dirian (University of Geneva)

Texas2015.pdf

17:53 Viability of a quintessence model with inverse power law potential as a dark energy candidate

The physical explanation of the dark energy as the responsible agent of the currently accelerated expansion of the Universe remains as one of the most challenging questions of the modern physcis. Besides the standard scenario (in which it is caused by a cosmological constant) there are other proposals which range from the introduction of new more or less exotic components, to modifications to the general relativity theory. Among these proposals, some quintessence models posses the desirable feature of being free of fine-tuning problems showing a dynamical behaviour clearly discernible from the LCDM model. In this poster we present an inverse-power-law-potential quintessence model inspired by a dynamically condensed Affleck-Dine-Seiberg superpotential. We show the basic phenomelogy predicted by this model and give contrains for its parameters using CMB information -WMAP 9yr & Planck- as well as supernovae Ia and BAO recent observations.

Speaker: Mr Erick Jonathan Almaraz Aviña (Instituto de Física / UNAM)

EAlmaraz_Poster.pdf

EAlmaraz_Talk.pdf

17:56 Constraints on a DE parametrization using BAO and Forecasting for future surveys

For this work a parametrization for the Dark Energy (DE) equation of state is proposed and tested. We derive constraints on our state equation parameters from the baryon acoustic oscillation (BAO) measurements. In particular we take advantage of high precision BAO measurements from galaxy clustering and the Lymann-$\alpha$ forest in the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS). Our analysis lead us to propose a DE fluid featuring a transition from a high redshift value of $w_i(z\gg0)$= - 0.96 to a $w_0$=-0.93 value at $z = 0$. The transition redshift is constrained to be as high as $z_T$ = 1.83. We find a good agreement of our model to the data, having a $\chi^2_{red} = 1.03$. Given the upmost importance of designing the future DE experiments (such as DESI) we provide a simple statistical analysis to forecast the required reduction in observational errors to distinguish between a Cosmological constant scenario and a time evolving DE model. Specifically we find that a reduction of 11% on the associated errors to $r_{BAO}(z)$ observational measurements is enough to exclude a cosmological constant at 1$\sigma$ of statistical significance in favor to our model and a 41% reduction would exclude the cosmological constant at 2$\sigma$ level.

Speaker: Ms Mariana Jaber (Universidad Nacional Autónoma de México)

poster_MarianaJaber.pdf

17:59 Force sensor for chameleon a candidate for dark energy

The search for non-Newtonian forces has been pursued following many different paths. Recently it was suggested that hypothetical chameleon interactions, which might explain the mechanisms behind dark energy, could be detected in a high-precision force measurement. In such an experiment, interactions between parallel plates kept at constant separation could be measured as a function of the pressure of an ambient gas, thereby identifying chameleon interactions by their unique inverse dependence on the local mass density. During the past years we have been developing a new kind of setup complying with the stringent requirements of the proposed experiment. In this poster we present the first and most important part of this setup—the force sensor. We discuss its design, fabrication, and characterization. From the results of the latter, we derive limits on chameleon interaction parameters that could be set by the forthcoming experiment. Finally, we describe the opportunity to use the same setup to measure Casimir forces at large surface separations with unprecedented accuracy, thereby potentially giving unambiguous answers to long-standing open questions

Speaker: attaallah almasi (vu university of amsterdam)

Table-top test of chameleon theories v1.pdf

talk- force sensor for Chameleon a candidate for dark energy.pdf

18:02 Exploring the consequences of parameter values in cosmological models with CosmoEJS, an interactive package of cosmology Java simulations

It is not only important to constrain the parameters of cosmological models with the most recent and precise observations, but it is also crucial to understand the physical consequences of those parameters for the different, but complimentary observations involved. CosmoEJS is an interactive Java package of simulations that allow the user to explore the ramifications of choosing various values for the cosmological parameters of a particular model. These simulations now include observations of the growth of structures of galaxies, as well as, the expansion history of the universe. Users can visually inspect the plotted theoretical values of their model, compare numerical fitting using $\chi^2$ values, calculate derived cosmological values, and finally plot the expansion trajectory of their models as they evolve in time.

Speaker: Jacob Moldenhauer (University of Dallas)

04_1802_Moldenhauer_Exploring_the_consequences.pdf

18:05 Testing the dark sector interaction by using the isolated galaxy pairs from SDSS DR10

By analyzing the spin alignment of isolated galaxy pairs from SDSS DR10 and in N-body simulation data for the coupled dark energy (cDE) model, we constrain the strength of dark sector interaction of cDE model. We perform Kolmogorov-Smirnov 2-sample tests to 6 different cases, one is the spin alignments from SDSS DR10 and in N-body simulation data for LCDM model, others are the spin alignments from SDSS DR10 and in N-body simulation data for cDE models with 5 different values of the strength of dark sector interaction. As a result, LCDM model and cDE model with zero dark sector interaction are the most consistent to SDSS DR10.

Speaker: Mr Hanwool Koo (Seoul National University)

18:08 The gravitational polarization of the quantum vacuum as a possible solution to the dark energy problem

Our study is based on the working hypothesis that by their nature quantum vacuum fluctuations are virtual gravitational dipoles. This hypothesis is the simplest solution to the cosmological constant problem and opens the possibility to consider the known Standard Model matter (i.e. matter made from quarks and leptons interacting through the exchange of gauge bosons) as the only content of the Universe. If this hypothesis is correct, each galactic halo of hypothetical dark matter must be replaced by the halo of the quantum vacuum polarized by the immersed baryonic matter. Totality of all these halos is a cosmological fluid which during expansion of the Universe converts from a fluid with negative pressure (allowing an accelerated expansion of the Universe) to a fluid with zero pressure (physically it means the end of the accelerated expansion). This for the first time suggests, at least mathematically, quantum vacuum may explain both phenomena; phenomena usually attributed to dark matter and phenomena usually attributed to dark energy.

Speaker: Dragan Hajdukovic (Institute of Physics, Astrophysics and Cosmology (ME))

DarkEnergy-Hajdukovic.pdf

DE-Hajduk.proc.pdf

18:12 Primordial perturbations in a bouncing Universe with quintessence

In this work we investigate the features of the primordial power spectrum when it arises from a contracting phase in the context of a bouncing Universe. We consider a toy model in which the Universe is dominated by a scalar field with an exponential potential, further on referred as the quintessence component. This choice is motivated by known results in the literature showing that such scalar field can behave like dust in the asymptotic past and asymptotic future, implying the generation of an almost scale invariant spectrum for large scale modes, but can also exhibit a dark energy behavior in between. The dynamical system analysis of the background equations shows that the scalar field experiences an effective equation of state of dark energy type either in the contracting phase or in the expanding phase of a quantum bouncing model, but not in both. The first scenario is an exercise about how a quintessence field playing the role of dark energy could add new features in the power spectrum if it was present in a contracting phase. The second is closer to realistic cosmological models where dark energy is present in the expanding phase, but is absent in the contracting phase. Both deserve attention, and are first approximations to the development of realistic approaches to adress the problem of structure formation in bounce cosmologies with dark energy.

Speaker: Anna Paula Bacalhau (Centro Brasileiro de Pesquisas Físicas)

primordial-perturbations-poster(1).pdf

18:15 Refinements of Jungle Universes

How effective barotropic matter can emerge from the interaction of cosmological fluids in an isotropic and homogeneous cosmological model ? The dynamics of homogeneous and isotropic Friedmann-Lemaître-Robertson-Walker universes is a natural special case of generalized Lotka-Volterra systems where each of the universe's fluid components can be seen as a competitive species in a predator-prey model. (Jungle universe arXiv:1306.1037v2) In addition to numerical simulations illustrating this behaviour among the barotropic fluids filling the universe, we analytically pinpoint that effective time-dependent barotropic indices can arise from a physical coupling between those fluids which dynamics could then look like that of another type of cosmic fluid, such as a cosmological constant. As the nature of dark energy still remains discussed today, this dynamical approach could help understanding some of the properties of dark matter and dark energy at large cosmological scales.

Speaker: Alicia Simon-Petit (Applied Mathematics Laboratory, ENSTA ParisTech, Université Paris-Saclay)

Alicia_Simon_Petit__Refinements_in_the_jungle__proceeding.pdf

18:18 gap

Tuesday 15 December

08:30 → 09:00 Registration

09:00 → 10:45 Plenary talks

09:00 A unifying description of dark energy

I will present an effective description of dark energy/modified gravity models involving a single scalar field. It is based on a 3+1 splitting of space-time with respect to uniform scalar field hypersurfaces. The advantage of this approach is that it can describe in the same language a vast number of existing models, including quintessence, F(R) gravity, Horndeski theories, as well as recently introduced scalar-tensor theories "beyond" Horndeski. This approach provides a unified treatment of linear cosmological perturbations, generically characterized by only five time-dependent functions. This gives an economic and systematic way to confront theoretical models with cosmological observations.

Speaker: David LANGLOIS (CNRS)

plenary_0900_Langlois_Unifing_Description_Dark_Energy.pdf

Video

09:35 Dark matter detection - an experimental overview

A major challenge of modern physics is to decipher the nature of dark matter. Astrophysical observations provide ample evidence for the existence of an invisible and dominant mass component in the observable universe, from the scales of galaxies up to the largest cosmological scales. The dark matter could be made of new, yet undiscovered elementary particles, with allowed masses and interaction strengths with normal matter spanning an enormous range. Axions, produced non-thermally in the early universe, and weakly interacting massive particles (WIMPs), which froze out of thermal equilibrium with a relic density matching the observations, represent two well-motivated, generic classes of dark matter candidates. Dark matter axions could be detected by exploiting their predicted coupling to two photons, where the highest sensitivity is reached by experiments using a microwave cavity permeated by a strong magnetic field. WIMPs could be directly observed via scatters off atomic nuclei in underground, ultra low-background detectors, or indirectly, via secondary radiation produced when they pair annihilate. They could also be generated at particle colliders such as the LHC, where associated particles produced in the same process are to be detected. After a brief introduction to the phenomenology of particle dark matter detection, I will discuss the most promising experimental techniques to search for axions and WIMPs, addressing their current and future science reach, as well as their complementarity.

Speaker: Prof. Laura Baudis (University of Zurich)

baudis_texas15.pdf

Video

10:10 Towards fundamental physics from cosmological surveys

Surveys of the cosmic microwave background and large galaxy surveys of the next decade carry immense promise for measurements of new physics beyond the Standard Models of cosmology and particle physics. However, these observations are complicated by multiple sources of systematics, either intrinsic, observational, or instrumental, which must be carefully controlled in order to make reliable inferences from the data about fundamental physics. In this talk I will show how some of these real-world effects impact the data. I will present an example of how spatially-varying observing conditions impact measurements of fundamental physics (such as primordial non-Gaussianity) from galaxy surveys, and discuss techniques that can be used to control these systematics. I will present a comprehensive survey of the capabilities of future CMB experiments, taking account of Galactic foregrounds and the effect of lensing by intervening large-scale structure. Incorporating these effects, I will present forecasts for the constraining power of these experiments in terms of inflationary physics, the neutrino sector, and dark energy parameters.

Speaker: Prof. Hiranya Peiris (University College London)

plenary_1010_Peiris_Towards_fundamental_question.key

plenary_1010_Peiris_Towards_fundamental_question.pdf

Video

10:45 → 11:20 Coffee break and poster session

11:20 → 12:30 Plenary talks

11:20 The equation of state of dense matter

With an average density higher than the nuclear density, neutron stars provide a unique test bed for nuclear physics, quantum chromodynamics, and nuclear superfluidity. Determination of the fundamental interactions that govern matter under such extreme conditions is one of the major unsolved problems of modern physics and - since it is impossible to replicate these conditions on Earth - a major motivation for future telescopes. Relativity, however, plays a key role in efforts to measure the equation of state. It is using relativistic effects that we measure neutron star mass and radius, and it is the relativistic equations of stellar structure that relate mass and radius to the equation of state. I will review our current state of understanding of the dense matter equation of state, and the prospects for better constraints to come from future telescopes.

Speaker: Prof. Anna Watts (University of Amsterdam)

plenary_1120_Watts_The_Dense_Matter.pdf

Video

11:55 Status of the Advanced Virgo project

The european detector Advanced Virgo is ending the installation phase and the plan is to run during 2016 joining the LIGO detectors installed in USA. Its improved sensitivity will increase the detection probability of GW events. In this talk we summarize the scientific outcome of the old network of advanced detectors in the past configuration. Then, we emphasize the potentialities of the new network in the context of the multimessenger astronomy. which will combine the GW information with those of the electromagnetic and neutrino signals likely emitted during the same astrophysical process.

Speaker: Prof. Fulvio Ricci (University of Rome La Sapienza and INFN Sez. Roma)

plenary_1155_Ricci_Gravitational_Waves.pdf

plenary_1155_Ricci_Gravitational_Waves.pptx

Video

12:30 → 14:00 Lunch break

14:00 → 15:45 13 - Gamma-ray bursts

Convener: Luigi Piro (National Institute for Astrophysics - INAF)

14:00 Short gamma-ray bursts from binary neutron star mergers: the time-reversal scenario

Leading models relate short gamma-ray bursts (SGRBs) to a relativistic jet launched by the black hole (BH)-accretion torus system that can be formed in a binary neutron star (BNS) or a NS-BH binary merger. However, recent observations by Swift have revealed a large fraction of SGRB events accompanied by X-ray afterglows with durations $\sim10^2-10^5$ s, suggesting continuous energy injection from a long-lived central engine that is incompatible with the short ($<\!1$ s) accretion timescale of a BH-torus system. The formation of a supramassive NS (SMNS), resisting the collapse on much longer spin-down timescales, can explain these X-ray afterglows as powered by the magnetic spin-down of the star, but leaves serious doubts on whether a relativistic jet can be launched at merger. Here we present a novel "time-reversal" scenario that can solve this dichotomy. In this scenario, the SGRB is produced *after* the eventual collapse of the SMNS to a BH, but observed *before* part of the long-lasting X-ray signal powered by magnetic spin-down.

Speaker: Dr Riccardo Ciolfi (University of Trento and INFN-TIFPA)

13_1400_Ciolfi_Short_gamma_ray_bursts.pdf

14:21 Electromagnetic emission from long-lived binary neutron star merger remnants

Recent observations indicate that in a large fraction of binary neutron star (BNS) mergers a long-lived neutron star (NS) may be formed rather than a black hole. Unambiguous electromagnetic (EM) signatures of such a scenario would strongly impact our knowledge on how short gamma-ray bursts (SGRBs) and their afterglow radiation are generated. Furthermore, such EM signals would have profound implications for multimessenger astronomy with joint EM and gravitational-wave (GW) observations of BNS mergers, which will soon become reality with the ground-based advanced LIGO/Virgo GW detector network starting its first science run this year. Here we present a model to bridge the gap between numerical simulations of the merger process and the relevant timescales for the afterglows, assuming that the merger results in a long-lived NS. It provides a self-consistent evolution of the post-merger system and its EM emission starting from an early baryonic wind phase and resulting in a final pulsar wind nebula that is confined by the previously ejected material. We present lightcurves and spectra and discuss these results in the context of SGRBs, their X-ray afterglows, and multimessenger astronomy.

Speaker: Mr Daniel Siegel (Max Planck Institute for Gravitational Physics (Albert Einstein Institute))

TexasSymposium2015_siegel.pdf

14:42 Dynamical mass ejection from black hole-neutron star binaries

In recent years, mass ejection from compact binary coalescences has been getting a lot more attention. Neutron-rich material ejected from neutron stars during such a coalescence event are increasingly recognized as the most promising site of the rapid process (r-process) nucleosynthesis. Mass ejection will also be the primary agent for driving electromagnetic radiation from compact binary mergers, or electromagnetic counterparts to gravitational waves. Simultaneous detection of electromagnetic counterparts with gravitational waves is eagerly desired, particularly for accurate source localization. Because mass ejection from black hole-neutron star binaries is a violent phenomenon involving disruption of neutron stars, numerical relativity is the only reliable approach for theoretical investigation. In this talk, we present our latest results for dynamical mass ejection from the black hole-neutron star binary merger obtained by numerical-relativity simulations. We also discuss possible electromagnetic counterparts from the anisotropic dynamical ejecta from black hole-neutron star binaries.

Speaker: Dr Koutarou Kyutoku (RIKEN)

Texas151215.pdf

15:03 Fast luminous blue transients from newborn black holes

Newborn black holes in collapsing massive stars can be accompanied by a fallback disc. The accretion rate is typically super-Eddington and strong disc outflows are expected. Such outflows could be directly observed in some failed explosions of compact (blue supergiants or Wolf-Rayet stars) progenitors, and may be more common than long-duration gamma-ray bursts. Using an analytical model, we show that the fallback disc outflows produce blue UV-optical transients with a peak bolometric luminosity of ˜ 1042-43 erg s- 1 (peak R-band absolute AB magnitudes of -16 to -18) and an emission duration of ˜ a few to ˜10 d. The spectra are likely dominated intermediate mass elements, but will lack much radioactive nuclei and iron-group elements. The above properties are broadly consistent with some of the rapid blue transients detected by Panoramic Survey Telescope & Rapid Response System and Palomar Transient Factory. This scenario can be distinguished from alternative models using radio observations within a few years after the optical peak.

Speaker: Dr Kazumi Kashiyama (University of California, Berkeley)

kashiyama.pdf

kashiyama.pptx

15:24 gap

14:00 → 15:45 15 - Binaries: ULX and LMXB

Convener: Alessandro Papitto

14:00 The ultraluminous pulsar

M82 X-2, an ultraluminous X-ray source in M82, was recently shown to harbor an accreting neutron star. Its luminosity being ~100 times the Eddington limit for a neutron star, it poses some problems to the existing theoretical framework about accretion onto neutron stars. I will talk about the proprieties and behavior of this source, how it was unveiled as a neutron star, the possible theoretical interpretations and some preliminary results coming from new observations of the M82 field.

Speaker: Matteo Bachetti (INAF/Osservatorio Astronomico di Cagliari)

M82_x2.pdf

14:25 Across the Eddington boundary: examining disc spectra at high accretion rates

There are now strong arguments that many ultraluminous X-ray sources (ULXs) are powered by super-Eddington accretion on to stellar remnant black holes. However, a key remaining question is: how are the classic sub-Eddington and new super-Eddington accretion states related? In an attempt to answer this, we present results from a systematic analysis of samples of the brightest thermal dominant (TD) black hole binaries (BHBs) and the faintest ULXs in the 0.3--10 keV band pass. We have previously shown that the faintest ULXs tend to have X-ray spectra that are disc-like, but broader than expected for thin accretion discs (broadened disc, or BD, spectra). Here we report that the TD BHB spectra are similar in shape to the BD ULXs in the 0.3--10 keV band, and differ only in luminosity, by a factor of $\sim 10$. This broadening may have been missed in previous studies that looked primarily above $\sim 2$ keV. As the Eddington ratios of the TD BHBs are well constrained to moderate values, known effects are not expected to produce such broad spectra. This implies there may be a missing physical mechanism in our best accretion disc models. We discuss the implications of our results for the BD ULXs. If they were at similar Eddington ratios to the TD BHBs, then they would most likely contain massive stellar remnant black holes. However, this would require that they were all at close to maximal spin. Instead, the BD ULXs could simply be a high Eddington ratio extension of the TD state.

Speaker: Andrew Sutton (NASA Marshall Space Flight Center)

15_1425_Sutton_Across_the_Eddington.pdf

14:50 Sub-Eddington accretion in neutron star X-ray binaries

I will present our results of our studies on the spectral properties of neutron star low-mass X-ray binaries when they have accretion luminosities between 1e34 and 1e36 erg/s (roughly 0.01 - 1 percent Eddington). We found that their photon index increases with decreasing 0.5-10 keV luminosity (the spectrum softens). Such behaviour has been reported for individual sources, but we now demonstrate that likely most systems behave in a similar manner. When comparing with black-hole systems, it is clear that most black-hole binaries have harder spectra at those luminosities. This suggests that the spectral properties at low luminosities can be used to determine the nature of the accretor in unclassified binaries. We suggest that this difference likely arise from the neutron-star surface becoming dominantly visible. We also suggest that both the thermal component and the non-thermal component might be caused by low-level accretion on the neutron star surface for luminosities below a few times 1e34 erg/s, contrary to the general believe.

Speaker: Rudy Wijnands (University of Amsterdam)

15_1450_Wijnands_Sub-Eddington accretion.pdf

15_1450_Wijnands_Sub-Eddington accretion.pptx

15:20 NuSTAR and XMM-Newton Observation of SAX J1808.4-3658 during the latest outburst

We will present spectral and timing analysis of NuSTAR and XMM-Newton data of the Accreting Millisecond Pulsar SAX J1808.4-3658 during its latest outburst in April 2015. We will discuss a high-quality broad band (2-80 keV) spectrum where the reflection component is clearly present, in line with previous results. Using DDT XMM-Newton data, we derived updated values for the spin and the orbital period of the source. We will discuss the secular evolution of these parameters in the framework of conservative versus non-conservative evolutionary scenarios.

Speaker: Prof. Tiziana Di Salvo (University of Palermo)

15_1520_Di Salvo_NuSTAR and XMM Newton.pptx

Millisec_Pulsar_Shot_1.mpg

plunge_i80l.mpg

14:00 → 15:45 16 - Black holes

Convener: Didier Barret (IRAP (UPS/CNRS))

14:00 XMM-Newton's impact on Relativistic Astrophysics: Black Holes

With about 300 refereed papers published each year, XMM-Newton is one of the most successful scientific missions of ESA ever. Observations of Galactic as well as supermassive black holes, where relativistic effects have to be accounted for, play a major role in XMM-Newton's observing program. The main focus of the talk will be the discussion of scientific highlight results based on XMM-Newton observations of compact, relativistic objects during the last years. X-ray observations provide a unique opportunity to study the vicinity of compact objects, i.e. the region where the strong gravitational field acts and allow the determination of black holes spin.

Speaker: Norbert Schartel (ESA)

16_1400_Schartel_XMM_Newton.pdf

16_1400_Schartel_XMM_Newton.ppt

rxj1242_tidal_disruption_lg.mpg

14:21 Relativistic tidal disruption events: what do we learn from their rate distribution?

We will report on the discovery potential of relativistic tidal disruption events with current and future instruments and its impact on the SuperMassive black hole mass function and the theory of jet formation. Relativistic TDEs (or jetted TDEs) are a new class of sources, recently discovered by Swift/BAT, showing a significant radio counterpart of a common tidal disruption event. Observing relativistic TDEs (from previously non-active galaxies) provides us with a new means of studying the early phases of jet formation and evolution in an otherwise pristine environment. Although several (tens) TDEs have been discovered since 1999, only three jetted TDEs have been recently discovered in hard X-rays, and two of them, Swift J1644+57 and Swift J2058+05, have a precise localization which further supports the TDE interpretation. We will discuss how the highest discovery potential for relativistic TDEs is not held by current and up-coming X-ray instruments (only a few to a few tens events per year expected) but by the Square Kilometer Array (SKA). We expect SKA to detect TDEs and trigger multi-wavelength follow-ups, yielding hundreds candidates per year even at high $z$. Radio and X-ray synergy, however, can in principle constrain important quantities such as the absolute rate of relativistic TDEs, their jet power, bulk Lorentz factor, the black hole mass function, and perhaps cover massive black holes with < 10^5 Msun.

Speaker: Immacolata Donnarumma (National Institute for Astrophysics - INAF)

16_1421_Donnarumma_Relativistic_Tidal_Distruption_Events.pdf

16_1421_Donnarumma_Relativistic_Tidal_Distruption_Events.pptx

14:42 Un-Beamed Tidal Disruption Events at Hard X-Rays

Thanks to their thermal emission, Tidal Disruption Events (TDEs) were detected regularly in the soft X-rays and sometimes in the optical. Only few of them have been detected at hard X-rays: two are high redshift beamed events, one occurred at the core of a nearby galaxy and the last one is of a different nature, involving a compact object in the Milky Way. The aims of presented work are to obtain a first sample of hard X-ray selected un-beamed TDEs, to determine their frequency and to probe if TDEs are usually or exceptionally emitting at hard X-rays. We performed extensive search for hard X-ray flares at the positions of over 53000 galaxies up to a distance of 100 Mpc in the Swift BAT archive. Light curves were extracted and parametrized. The quiescent hard X-ray emission was used to exclude persistently active galactic nuclei. Significant flares from non-active galaxies were derived and checked for possible contamination. We found a sample of nine TDE candidates, which translates in a rate of $2 \times 10^{-5}$ galaxy$^{-1}$ yr$^{-1}$ above the BAT detection limit. This rate is consistent with these observed by XMM-Newton at soft X-rays and in the optical from SDSS observations, and expected from simulations. We conclude that hard X-ray emission should be ubiquitous in un-beamed TDEs and that electrons should be accelerated in their accretion flow.

Speaker: Krzysztof Hryniewicz (Nicolaus Copernicus Astronomical Centre)

16_1442_Hryiewicz_Un_Beamed_Tidal.pdf

15:02 IGR J17361-4441: a possible planetary tidal disruption event in NGC 6388

In 2011 a new hard X-ray source, IGR J17361-4441, was discovered by INTEGRAL close the centre of the globular cluster NGC 6388. Based on its peak luminosity, it was classified as very faint X-ray transient. A Swift/XRT monitoring campaign showed an evident t^(-5/3) trend in the light curve, and a thermal emission of ˜˜˜˜~0.08 keV that did not evolve significantly with time. We investigated whether this source could be a tidal disruption event, and for certain assumptions, we found an accretion efficiency consistent with a massive white dwarf and a disrupted minor body mass ˜˜˜˜~2E+27 M/M_Ch g in the terrestrial-icy planet regime. Although the density of white dwarfs and the number of free-floating planets are uncertain, we estimated the rate of planetary tidal disruptions in NGC 6388 to be in the range 3E-6 up to 3E-4 yr^(-1). Averaged over the 150 globular clusters in the Milky Way, the upper limit value corresponds to 0.05 yr^(-1), consistent with the life-time of INTEGRAL and Swift.

Speaker: Dr Melania Del Santo (National Institute for Astrophysics - INAF)

16_1502_Del_Santo_IGR_J17361_4441.pdf

15:22 Relativistic line reverberation mapping in tidal disruption events

When normal stars run close enough to the previously dormant supermassive black holes (SMBHs) at the centres of normal galaxies, they would be entirely or partly disrupted due to the tidal force, leading to the so-called tidal disruption events (TDEs). Part of the debris material will be accreted by the SMBHs later on. The accretion of the debris material would generate X-ray flares, which will illuminate the remaining debris material and would generate spectral line feature in their spectra. Here we show predicted features due to relativistic spectral lines expected to occur during the accretion phase of the debris material. We demonstrate that these spectral features can be used to probe the mass and spin of the SMBHs at the centres of galaxies as well as the accretion geometry and GR effects involved in the TDE events.

Speaker: Wenfei Yu (Shanghai Astronomical Observatory)

16_1522_YU_Relativistic_line_reverberation_mapping_in_tidal_disruption_event.key

16_1522_YU_Relativistic_line_reverberation_mapping_in_tidal_disruption_event.pdf

15:42 Tidal disruption events induced by the Kozai-Lidov mechanism

We geometrically analyze the evolution of the Kozai-Lidov mechanism induced by an infalling tertiary. This approach enables us to clearly understand how the inner orbits are deformed, in response to the time variation of the related phase-space structure. We predict that, in a stellar cluster associated with massive black hole binaries, a constituent star could abruptly become highly eccentric, because of a peculiar bifurcation pattern.

Speaker: Naoki Seto

seto.pdf

14:00 → 15:45 18 - Gal. accel. & pulsars: Pulsars

Convener: Marco Tavani (INAF)

14:00 Numerical Models For Superfluid Neutron Stars With Realistic Equation Of State And Application To Pulsar Glitches

We present a realistic numerical model for rotating superfluid neutron stars in a full general relativistic framework. Following the work initiated by Prix, Novak & Comer [1], we compute stationary axisymmetric configurations of neutron stars composed of two fluids, namely superfluid neutrons and charged particles (protons and electrons), which are free to rotate around a common axis with different rigid rotation rates. This system is described by a realistic equation of state derived from a relativistic mean field theory using DDH parametrization including (or not) delta mesons. Then, we apply this model to investigate pulsar glitches in a very simple way. From a series of equilibrium states of a neutron star, assuming total baryon mass and total angular momentum to be constant, we compute the evolution in time of the properties of the star during a glitch. To do so, we model a glitch as a transfer of angular momentum from one fluid to the other, through the action of mutual friction force [2]. This enables us to infer characteristic features relative to glitches, such as rise timescales, which could be compared to future accurate observations. [1] Prix, R., Novak, J. & Comer, G. L., Relativistic numerical models for stationary superfluid neutron stars, Phys. Rev. D 71, 2005 [2] Langlois, D., Sedrakian, D. M. & Carter, B., Differential rotation of relativistic superfluid in neutron stars, MNRAS 297, 1998

Speaker: Aurélien Sourie (LUTH - Observatoire de Paris)

sourie.pdf

14:21 Multi-scale modelling of pulsar glitches

Neutron stars are an exceptional fundamental physics laboratory, and provide us with the only opportunity to study the strong interaction at high densities and low temperatures. These objects are, in fact, not only very dense (with central densities surpassing nuclear saturation density), but also cold, as their thermal energy is generally negligible compared to the Fermi energy of the constituents. This will modify the dynamics of the system considerably, with large scale superfluids expected in the interior. Observations of radio pulsar glitches offer what is considered to be a probe of the dynamics of the superfluid in NS interiors. Glitches, i.e. sudden jumps in the spin frequency of the pulsar, are generally thought to be due to a large scale superfluid component that is decoupled from the spin-down of the 'normal' component, and then recouples catastrophically, giving rise to the observed signal. This is a fascinating macroscopic effect of small scale, quantum, properties of a superfluid. A superfluid rotates by forming an array of quantised vortices, which can 'pin' to ions in the crust or flux-tubes in the core, preventing the superfluid neutron component from expelling vorticity and spinning down with the rest of the star. Previous work has been successful in separately modelling vortex motion on microscopic scales and the large scale hydrodynamics of the star. In this talk I will present recent work that aims to bridge this gap in scales and consistently model the whole glitch process. I will discuss analytical and numerical work to extend the results of small scale quantum mechanical simulations to larger scales, and how these results can be used in hydrodynamical simulations, possibly to explain the recently observed size distribution of glitches in the Crab pulsar.

Speaker: Brynmor Haskell (The University of Melbourne)

18_1421_Haskell_Multi_scale_modeling.key

18_1421_Haskell_Multi_scale_modeling.pdf

14:42 The role of general relativity and reconnection in pulsar radiation

Pulsars shine throughout the electromagnetic spectrum, from radio waves to energetic gamma rays. The radio emission is thought to originate from the discharge of the polar-cap and the formation of copious electron-positron pairs. Gamma rays are traditionally associated with particle acceleration in electrostatic gaps within the light cylinder. The recent development of global Particle-In-Cell (PIC) simulations of the pulsar magnetosphere enables to test these scenarios self-consistently. We show that general relativistic effects, most notably frame-dragging, are essential to ignite pair creation in the polar cap for low-inclination pulsars, and hence enable pulsars to emit radio waves. In addition, three-dimensional radiative PIC simulations indicate that the current sheet that forms beyond the light cylinder is the main site of particle acceleration in plasma-filled pulsars, instead of gaps within the co-rotating magnetosphere. Relativistic reconnection dissipates the magnetic energy which is then converted to energetic particles and high-energy synchrotron radiation. We present self-consistent modeling of pulsar gamma-ray lightcurves and spectra obtained directly from the kinetic simulations, and discuss the results in the context of observed gamma-ray pulsars.

Speaker: Benoit Cerutti (Princeton University)

bcerutti_Texas2015.pdf

bcerutti_Texas2015.ppt

15:02 The shape of a pulsar radio beam: fan beams, not the nested cones.

The knowledge of radio emission geometry is crucial for interpreting their gamma-ray profiles, and for establishing the orientation of their tilted magnetic field. I will review the continually increasing evidence against the most popular (nested cone) radio beam geometry. It will be shown that several features of pulse profiles, which have normally been considered as signatures of the nested cones, can in fact be readily interpreted through a system of fan beams. These include some properties of the radius-to-frequency mapping as well as the special-relativistic lag of the core component in multicomponent profiles. A new statistical probe of beam shape will be introduced, based on the ratio of component separations observed in M and Q profiles. This method is independent of the parameters that determine the scale of the beam (emission altitude, frequency, rotation period, dipole tilt) while it retains the sensitivity to the beam shape. When applied to the Q and M pulse profiles, the method reinforces the problems of the conal geometry and favours the azimuthally-structured beam (a system of fan beams). The non-conal geometry has consequences for the gamma-ray profile modelling.

Speaker: Dr Jaroslaw Dyks (Nicolaus Copernicus Astronomical Center)

dyks_geneva.pdf

proc_dyks_geneva.pdf

15:22 A new view on the Lighthouse Nebula, IGR J11014-6103

Despite jets are detected in all kind of accreting systems, bright and elongated jets are known to be formed also by isolated rotationally powered pulsars. PSR J1101-6101 in the Lighthouse Nebula is an isolated pulsar which is powering a bright wind nebula and two jets, while travelling at supersonic velocity in the interstellar medium. Extending over 15 pc, the jets are more than 10 times longer than the well known Crab pulsar's jets, and are the most elongated X-ray jet(s) seen in our Galaxy. Unexpectedly, the jets are perpendicular to the direction of motion. The wind nebula is tracing the passage of the pulsar in the medium, pointing back to its parent supernova remnant. The latest data obtained with the Chandra X-ray Observatory give a fresh view on this system. The imaging capabilities of Chandra were used to pinpoint the launching site of the outflows. The new data are enlightening spatial and spectral properties of the jets and of the wind nebula.

Speaker: Lucia Pavan (University of Geneva)

Lpavan-texas2015.pdf

15:42 A model for distortions of polarisation angle in radio pulsars

Average profiles of some radio pulsars contain weak emission components which cover large intervals of pulse phase as well as localised emission or absorption features. The polarisation-angle (PA) under such features exhibits local distortions which cannot be explained through the rotating vector model and other effects such as the special relativistic effects or modification of magnetic fields. We show that some of these distortions in the average PA curve can be explained using a simplified physical model of an extended microbeam of the X-mode curvature radiation. Successful interpretation will be presented for features with very different polarisation characteristics, such as the bifurcated emission component on the trailing side of the profile of J0437-4715, and for the double notches observed in B1821-24A and J0437-4715.

Speaker: Lab Saha (Nicolaus Copernicus Astronomical Center, Torun, Poland)

LabSaha_poster.pdf

Lab_Saha_teaser.pdf

LabSaha_Texas2015_proc.pdf

14:00 → 15:45 10 - Cosmic magnetic fields: Probes

Convener: Tina Kahniashvili

14:00 Cosmic magnetic fields and ways of probing them

A non-negligible fraction of a Supermassive Black Hole's (SMBH) rest mass energy gets transported into extragalactic space - by remarkable processes in jets which are not completely understood. The bulk of the energy flow from the SMBH (e.g. $10^7$ M$_\odot$) appears to be electromagnetic, rather than via a particle beam flux. Also, remarkably, these jets contain current flows that remain largely intact over multi-kpc distances. Accretion disk models have independently calculated that a $\sim 10^8$ M$_\odot$ SMBH should generate O(10$^{18 - 19}$) Ampères in the vicinity of the SMBH. I describe the best yet observational estimate of the current flow along the axis of a jet that extends from the nucleus of the active elliptical galaxy in 3C303. This is I $\sim 10^{18}$ Ampères at a projected 20 kpc from the AGN. This points to the existence of cosmic scale electric circuits. The power flow is P = I$^2$Z, watts, where Z $\sim 30$ Ohms, which is O (the impedance of free space), Z ($\epsilon_0$, $\mu_0$), where ($\epsilon_0$, $\mu_0$) are the permittivity and magnetic permeability. These, in turn, uniquely determine c. The electrical potential drop ($\sim 10^{20}$ V) across the jet diameter (which is  a few times rG of the SMBH) is, interestingly  that required to accelerate Ultra High Energy Cosmic Rays (UHECR). Jets and high energy outflows have different progenitors, forms, sizes, luminosities, and ambient environments. This talk focuses on electromagnetically dominated (Poynting flux) jets from supermassive BH’s located in a rarified intergalactic environment - i.e. not in rich galaxy clusters.

Speaker: Prof. Philipp Kronberg (University of Toronto)

KRONBERG_TEXAS_GENF-2015WEBminus_extras.pdf

14:25 Galactic magnetic fields

This talk will provide an overview of our current knowledge about galactic magnetic fields. The typical properties of magnetic fields in galactic discs and halos will be described as well as magnetic field characteristics at different length scales between 10 pc and 10 kpc. The talk will concentrate on reviewing what is known from observations, but will also point out the areas where theoretical models have been successful and where they still face challenges. I will briefly discuss the prospects for exciting new developments in our understanding of galactic magnetic fields and their evolution, due to the improvement in radio telescope capabilities that is currently underway.

Speaker: Andrew Fletcher

10_1425_Fletcher_Calactic_magnetic_fields.pdf

14:45 Probing the Intergalactic Magnetic Fields by means of high-energy pair halos around extreme blazars

The origin of cosmic magnetic fields permeating galaxies and clusters is still unknown.To undertstand the origin and the evolution of the primordial cosmic magnetic fields we need to probe the existence and to characterize magnitude and correlation length of magnetic field in voids (Intergalactic magnetic field, IGMF), where pollution from magnetic fields associated to structures is expected to be minimal. Techniques like Faraday Rotation and Zeeman splitting permit to compute upper limits on IGMF of the order of 10^-9 G. Nevertheless our knowledge on IGMF is still poor. Very High Energy (VHE) photons (E>50 GeV) coming from extreme Blazars interact with Optical/Infrared Extragalactic Background Light (EBL). Because of these interactions electron-positron pairs are produced. These, in turn, upscatter via inverse Compton the CMB photons producing a reprocessed emission. If the primary photons have energies higher than 10 TeV this component will be in the GeV domain. IGMF deflects the pairs so this component will be in the form of extended emission whose angular extension depends on the strength of IGMF. The detection of this component is an unique tool to measure the IGMF. The measurement of halo emission by Cherenkov telescopes like MAGIC depends strictly on its capability to disentangle the extended from the point-like emission of the source. For the first time the detailed characterization of the PSF of MAGIC has allowed to assess the possibility to reveal the extended emission due to IGMF. We first found a good analytical model for the MAGIC PSF and then, comparing the emission profiles of several AGN with the PSF reference, we obtained that all souces are point like. Using two different halo emission models we computed for all sources upper limits on extended emission. For the source Markarian 421 our procedure provided an upper limit which is more than three times better than a previous published measurement. In addition we found that the sources 1ES 0229+200 and RX J1136.5+6737 though well described by a point-source profile, do not exclude the presence of extended emission. In this case the implied strenghts of IGMF are of the order of 10^-14 G.

Speaker: PAOLO DA VELA (INFN - National Institute for Nuclear Physics)

Texas_2015_IGMF_v5.pdf

15:05 Lower limits on the magnetic field strength in the early universe

Two recent estimates of lower limits for the stochastic primordial magnetic fields are reviewed. The first estimate pioneered by Neronov and Vovk (2010) is based on GeV-TeV $\gamma $-ray observations of distant blazars by air-Cherenkov telecopes and the FERMI satellite. The generated $e^{\pm }$ pair beams from double photon collisions with the extragalactic background light have been expected to initiate a full electromagnetic cascade as in vacuum. However, as the cascaded GeV inverse Compton scattered gamma-rays have not been detected, the existence of small irregular intergalactic magnetic fields, scattering the produced pairs, has been predicted. However, the generated initial pair beams are subject to rapid electrostatic and electromagnetic kinetic plasma instabilities (Broderick et al. 2012, Schlickeiser et al. 2012) in the unmagnetized fully-ionized intergalactic medium, so that less kinetic initial pair energy for the cascade emission is available, explaining the non-detected GeV $\gamma $-rays. The second estimate calculates the magnetic (and electric) equilibrium wavenumber spectrum of aperiodic collective fluctuations in the thermal isotro\-pic electron-proton intergalactic plasma using the generalized Kirchhoff laws, accounting self-consistently for the simultaneous competition of spontaneous emission and absorption processes. By integrating the wavenumber spectrum over all wavenumber values provides for the total magnetic field strength in the IGM $|\delta B|=\sqrt{(\delta B)^2}\simeq 10^{-17}$ G with maximum length scales $\le 10^{15}$ cm. This guaranteed magnetic field in the form of randomly distributed aperiodic fluctuations, produced by the spontaneous emission of the isotropic thermal IGM plasma, sets a robust lower limit on stochastic primordial magnetic fields, and serves as seed field for amplification by later possible plasma instabilities from anisotropic plasma particle distribution functions, MHD instabilities and/or the MHD dynamo process.

Speaker: Prof. Reinhard Schlickeiser (Ruhr University Bochum, Germany)

10_1505_Schlickeiser_Lower_limits_on_the_magnetic_field_strength.pdf

15:25 The Plasma Physics of TeV Blazars

Constraints on the primordial intergalactic magnetic field from the non-observation of inverse Compton cascades around extragalactic very high energy sources, i.e., the TeV blazars, assume that inverse Compton scattering is the dominant physical mechanism by which dilute ultrarelativistic pair beams lose their energy. Over the last few years, we have considered the effect of plasma instabilities on these ultrarelativistic beams. We argue that the linear growth rate of these instabilities, and in particular the oblique instability, are so fast that these instabilites may dominate the cooling of these pair beams leading to an order of magnitude or more suppression in the inverse Compton cascade. We review the relevant physics of these plasma instabilities and discuss the linear instability of these pair beams. We also discuss recent work on the various nonlinear aspects of this instability and the effect of density gradients on the instability. We highlight the effect of this instability on the constraints of the intergalactic magnetic field, arguing that these constraints are precluded in the presences of these instabilities. We also discuss the implication of these instabilities on the population of TeV blazars, and the intergalactic gamma ray background. Finally, we close with a discussion on the effect of these extra blazar heating on cosmological structure formation, in particular, the temperature-overdensity profile and the Lyman-alpha forest.

Speaker: Philip Chang

TeV Texas Symposium.key.zip

TeV Texas Symposium.pdf

TeV Texas Symposium.pdf

14:00 → 15:45 09 - Cosmic neutrinos

Convener: Julien Lesgourgues

14:00 Joint Constraints on Neutrino Masses from Cosmology and Particle Physics

The absolute scale of neutrino masses is one of the main open issues both in cosmology and particle physics. Current experimental strategies involve i) measurements exploiting kinematics effects in beta decay, ii) searches for neutrinoless double beta decay ('0n2b'), and iii) cosmological observations. The three approaches are complementary, each of them presenting its own advantages and disadvantages, and also because they are sensitive to slightly different quantities related to the neutrino masses. In this work, we want to derive joint constraints on neutrino mass parameters from the most recent observations from both laboratory and cosmological experiments, and forecasts, combining them in the framework of Bayesian statistics. In particular, for '0n2b' experiments, we take into account the uncertainty related to nuclear matrix elements, in order to account its impact on the neutrino mass estimates.

Speaker: Martina Gerbino (University of Rome 'Sapienza')

09_1400_Gerbino_Joint_Constraint.pdf

14:21 Clustering, lensing, and ISW-RS from the DEMNUni neutrino simulations

I will present the first set of cosmological simulations produced within the “Dark Energy and Massive Neutrino Universe” (DEMNUni) project. These simulations are characterized by L=2 Gpc/h, Npart=2 x 2048^3, a baseline LCDM-Planck cosmology, and four different total neutrino masses, Mnu=0, 0.17, 0.3, 0.53 eV, with a degenerate mass spectrum. They are the largest N-body simulations to date with a massive neutrino component treated as an additional particle type. I will present fully non-linear effects in the presence of massive neutrinos, extracted from the DEMNUni simulations, and show how neutrino free-streaming alters not only LSS clustering and lensing, but introduces also an excess of power in the ISW/RS signals, and related cross-correlations, at intermediate scales.

Speaker: Dr Carmelita Carbone (National Institute for Astrophysics - INAF)

TEXAS_Geneva_15Dec2015.pdf

14:42 Simulating the effect of massive neutrinos on large-scale structure

The massive neutrino background makes up a component of the dark matter, and as such affects the growth of large-scale structure, such as galaxy clusters. This affords us an opportunity to measure the neutrino mass. However, to do this we must accurately and efficiently characterize how neutrinos affect structure growth. I will describe a new method for including massive neutrinos in N-body simulations which is uniquely accurate in the limit of small neutrino masses, and incurs no cost above that of the N-body simulation. It uses perturbation theory for the neutrinos, modified to include source terms for the non-linear dark matter clustering. A small fraction of low-energy neutrinos which cluster more strongly may be treated as particles, but this does not substantially affect the overall structure.

Speaker: Dr Simeon Bird (Johns Hopkins University)

09_1442_Bird_Simulating_the_effect_of_massive_neutrinos.pdf

09_1442_Bird_Simulating_the_effect_of_massive_neutrinos.pptx

15:03 Neutrino masses and cosmology with Lyman-alpha forest power spectrum

I will present the constraint on massive neutrinos that was obtained recently using Lyman-alpha forest, BAO and CMB data. I will first describe the measurement of the power spectrum in the Lyman-alpha forest observed in quasars of the SDSS/BOSS survey. I will then present the extensive suite of N-body/hydro simulations that has been developed specifically for the purpose of this study, and show how it can be used to place constraints on the sum of the neutrino masses at the level of 0.12 eV (95% confidence level). I will also discuss the impact of Ly-alpha forest on the measurement of the primordial fluctuations by CMB experiments. Finally, I will illustrate how these data and simulations can also constrain the mass of neutrinos considered as Warm Dark Matter.

Speaker: Christophe Yeche

Neutrino_mass_ChY_Texas_Symposium.pdf

Proceeding_Neutrinos_Ly-a_Yeche.pdf

15:24 Massive neutrinos and their effect on the large scale structure of the Universe

Neutrinos are described as fundamental particles by the standard model of particle physics. The fact that neutrinos are massive, as demonstrated by neutrino oscillations experiments, point towards physics beyond the standard model. Thus, one of the most important questions in modern physics is: which are the masses of the neutrinos? Current tightest constrain on the sum of the neutrino masses arise from cosmology observables. In order to extract the maximum information from current and future surveys, as well as to avoid introducing biases in the values of the cosmological parameters, it is of primordial importance to understand, both at the linear and at the fully non-linear order, the impact that massive neutrinos induce on the distribution of matter, halos and galaxies. Among the different methods that can be used to carried out this task, N-body simulations offer the most accurate picture. In this talk I will show how to run N-body simulations in cosmologies with massive neutrinos. I will also present some of the effects neutrinos induce on the Universe large scale structure, among then the clustering of matter, the clustering of dark matter halos, the abundance of halos, the abundance of voids, their impact on the BAO peak and so on.

Speaker: Francisco Villaescusa-Navarro (OATS-INAF)

09_1524_Villaescusa_Massive_Neutrinos.pdf

09_1524_Villaescusa_Massive_Neutrinos.pptx

14:00 → 15:45 19 - VHE & CR: Blazars and EBL

Convener: Teresa Montaruli

14:00 Probing the Extragalactic Background Light with VERITAS

The observed spectra of active galactic nuclei carry the imprint of gamma-ray interactions with the extragalactic background light (EBL). As gamma rays from an extragalactic source travel to the observer, pair production on the EBL plays a role in reprocessing the photons to lower energies, obscuring the intrinsic source spectrum. VERITAS, a ground-based imaging atmospheric-Cherenkov telescope array sensitive to gamma rays above 85 GeV, has collected a large set of observations of blazars for a range of redshifts. We present the latest VERITAS results from using blazar spectral measurements to constrain the EBL’s spectral energy distribution.

Speaker: Elisa Kay Pueschel (University College Dublin)

Pueschel_VERITAS_EBL.pdf

14:21 Broadband characterisation and physical implications from the most extreme X-ray flaring activity of the high-peaked BL Lac Mrk 501

The high-frequency-peaked BL Lac object Markarian 501 is a very high energy (VHE, E>100 GeV) emitter located in our extragalactic neighborhood (z=0.034). The source can be detected in the VHE band during low state, what makes this target an ideal source for long-term multi-wavelength studies covering the entire electromagnetic spectrum. During a multi-wavelength campaign in 2014, the source showed the highest X-ray activity observed by Swift-XRT during the last decade. The source displayed very hard spectra at X-rays and gamma-ray energies with variability on day timescales. The distortion of the broadband SED strongly suggests the existence of, at the very least, an extra component with ultra-energetic and relatively narrow electron energy distribution, which had never been seen before for Mrk501. In the conference I will report about this unprecedented flaring event and its physical implications.

Speaker: Josefa Becerra Gonzalez (NASA GSFC)

19_1442_Becerra_Gonzalez_Broadband_charcterisation.pdf

14:42 Very fast TeV gamma-ray variability from the non-aligned AGN IC 310: Insight into Black Hole Lightnings

Rapid flux variabilities with time scales of minutes are regularly detected in the very high energy (VHE) gamma-ray emission of blazars during violent flaring periods. Those are generally explained by the classical shock-in-jet acceleration models, assuming a very large Doppler factor, which condenses the intrinsic multi-hours-scale variations into a few minutes for the observer on Earth. This assumption, which requires a large jet Lorentz factor (>10) and very small angle between the jet and the observer (<5 deg), is conceivable for blazars. However, recent observation of rapid variabilities in the VHE gamma-ray flux from the peculiar radio galaxy IC 310 by MAGIC is very challenging for the shock-in-jet model. Indeed the jet viewing angle is estimated to lie between 10 and 20 deg, and the Doppler boost cannot play a dramatic role. The flux doubling-time measured in November 2012 is faster than 5 min and constrains the size of the emission region to be smaller than 20% of the gravitational radius of the central black hole. Here, we will present in detail the MAGIC observations and discuss possible alternative models, such as pulsar-like particle acceleration in the magnetosphere anchored to the plasma surrounding a spinning black hole.

Speaker: Pierre Colin (MPI fuer Physik)

IC310_Texas2016_colin.pdf

15:03 A bright gamma-ray flare from the blazar B2 1215+30 detected by VERITAS and Fermi-LAT

We report on evidence of simultaneous gamma-ray flaring from the BL Lac source B2 1215+30, detected by VERITAS (E > 100 GeV) and the Fermi Large Area Telescope (100 MeV < E <100 GeV). The source was observed by VERITAS during an exceptional flaring state in 2014 February 08. Investigations of flux variability in the energy range covered by Fermi-LAT, show that the GeV flare occurred contemporaneously with the TeV flare. From the variability time scale we constrain the size of the emission region and derive a limit on the Doppler factor of the relativistic jet of B2 1215+30.

Speaker: Floriana Zefi (LLR - Ecole Polytechnique)

abstract.pdf

fzefi_b2_1215+30_Slides.pdf

15:24 Non-thermal particle acceleration in astrophysical shear flows.

The non-thermal radiation seen from astrophysical objects bears witness to the presence of energetic charged particles that have experienced efficient acceleration within these sources. Shear flows are naturally expected in many of these environments. Combined with new observational results in the radio and high energy gamma-ray domain and with progress in our understanding of turbulence modelling, this has given fresh impetus to shear acceleration and emission scenarios. Here we will review key results concerning the stochastic acceleration of energetic electrons and protons in gradual shear flows, highlight expected spectral characteristics and report on recent applications in the context of expanding relativistic outflows.

Speaker: Frank Rieger (MPIK and Univ. of Heidelberg)

Rieger_Texas15.pdf

14:00 → 15:45 04 - Dark energy

Convener: Martin Kunz (Universite de Geneve (CH))

14:00 Planck 2015 results on Dark Energy and Modified Gravity

The latest cosmic microwave background data obtained by ESA Planck satellite allow us to test the evolution and content of the Universe in great detail. I will review the analysis done by the Planck collaboration and presented in the "Planck 2015 results. XIV. Dark energy and modified gravity" paper, which considered two broad cases: a DE which affects the background evolution and DE or MG parametrizations which instead modify the evolution of cosmological perturbations. In this talk I will also discuss the combination of Planck data with external datasets and their implication on the constraints.

Speaker: Matteo Martinelli (ITP, Heidelberg)

martinelli_DE.pdf

14:26 Tensions Between CMB and Weak Lensing Data Sets when Testing General Relativity

There has been quite a bit of recent discussion about tension between CMB and weak lensing data sets, especially in the context of testing general relativity using modified growth parameters. We use a combination of cosmological data sets, including the CMB temperature anisotropy data from Planck, weak lensing tomography from CFHTLenS, and the WiggleZ galaxy power spectrum to place constraints on modified growth parameters. A likelihood analysis is performed using the publicly available package ISiTGR. We explore what tensions, if any, are present between the CMB and weak-lensing data when using three different parameterizations for the modified growth parameters.

Speaker: Jason Dossett (INAF - Osservatorio Astronomico di Brera)

04_1426_Dossett_Tensions_between_CMB.pdf

04_1426_Dossett_Tensions_between_CMB.ppt

14:53 Constraints on induced gravity dark energy models

We study the predictions for structure formation in an induced gravity dark energy model with a quartic potential. By developing a dedicated Einstein-Boltzmann code, we study self-consistently the dynamics of homogeneous cosmology and of linear perturbations without using any parametrization, accurately recovering the quasi-static analytic approximation in the matter dominated era. We use CMB anisotropies data and a compilation of BAO data to constrain the coupling $\gamma$ to the Ricci curvature and the other cosmological parameters. By connecting the gravitational constant in the Einstein equation to the one measured in a Cavendish-like experiment, we find $\gamma < 0.0012$ at 95 % confidence level with Planck 2013 and BAO data, and present the updated Planck 2015 constraint. Because of a degeneracy between $\gamma$ and the Hubble constant $H_0$, we show how larger values for $\gamma$ are allowed, but not preferred at a significant statistical level, when local measurements of $H_0$ are combined in the analysis with Planck data. We also extend the analysis and constraints to a simple monomial potential with a positive exponent.

Speaker: Mario Ballardini (University of Bologna)

Ballardini_ConstraintsOnInducedGravityDarkEnergyModels_Texas28.pdf

InducedGravity_proc.pdf

15:19 Cold dark energy and cosmological parameter estimation

Cold (or clustering) dark energy models present an interesting phenomonology in comparison to standard homogeneous dark energy. We investigate the impact of cold dark energy on the background evolution, on the linear level, as well as at the nonlinear level on structure formation. For an accurate description at the nonlinear level, the halo mass function is carefully recalibrated to include the effect of dark energy perturbations, employing the spherical collapse formalism. Using our MCMC likelihood analysis of X-ray cluster samples together with standard cosmological data sets, we constrain cosmological parameters when incorporating these non-linear corrections. We emphasize the impact on the constraints of the cosmological parameters when taking into account dark energy perturbations for cold dark energy.

Speaker: Caroline Heneka (Dark Cosmology Centre, Copenhagen)

04_1519_Heneka_Cold_Dark_Energy.pdf

15:45 → 16:15 Coffee break and poster session

16:15 → 18:45 .

16:15 → 18:45 15 - Binaries: ULX and LMXB

Convener: Alessandro Papitto

16:15 Hot Plasma Emissions in the Ultra-compact Binary Pulsar 4U 1626-67

4U 1626-67 is an ultra-compact binary pulsar with a pulse period of 7.7 sec and an orbital period of 40 min. Its X-ray spectrum varies distinctively before and after torque reversal episodes. 4U 1626-67 is a peculiar ultra-compact binary in that it not only truncates its accretion disk at the magnetospheric radius, but also emits Ne and O Doppler X-ray lines, The nature of these lines have remained quite mysterious but we can now show that these lines originate from a coronal type plasma with temperatures up to 10 Million degrees located at the magnetospheric radius. We also observe consistent variations in the disk lines before and after torque reversal. The observed disk lines constrain the angle of inclination to 38 degrees, which is is significally larger than previously assumed. We discuss these findings in the context of accreting X-ray binaries and binary pulsar properties.

Speaker: Norbert S. Schulz (Massachusetts Institute of Technology)

15_1615_Schulz_Hot Plasma.pdf

16:35 Luminosity dependent change of the emission diagram in the X-ray pulsar 4U 1626-67

We have discovered strong indications of a correlation between the appearance of the Fe Kα emission line in the spectrum of the X-ray pulsar 4U 1626-67 and its luminosity and shape of its pulse profile. Spectroscopic analysis of the latest, simultaneous Chandra/RXTE observation of 4U 1626-67, revealed the presence of a narrow Fe Kα emission line. The observation was performed when the source was in a high luminosity (> 10^37 erg/s) state. This feature was not present in previous Chandra and XMM-Newton observations, performed when the source was in a low luminosity regime. Timing analysis of archival XMM-Newton and RXTE data also revealed a major change in the pulse profile of the source. Namely, the pulse profile during the Chandra/RXTE, high luminosity, observation has a characteristic double peaked shape that is radically different from the pulse profile during the XMM-Newton observation when the luminosity was lower and the Fe line was not present. The iron line parameters are consistent with reflection of X-ray radiation off an accretion disk truncated close to the magnetospheric radius of a high field pulsar (B~10^12 Gauss). Furthermore, using our X-ray diagnostics method (Koliopanos et al. 2013 [1]), we showed that the relative faintness of the emission line, is consistent with reflection off a C/O rich disk, as expected for this system. We argue that the appearance of the line and the change in the shape of the pulse profile are correlated and are the result of a major modification of the emission diagram of the accretion column, from a pencil beam to a fan beam pattern. This change was caused by an increase in the mass accretion rate, as was theoretically predicted by Basko & Sunyaev in 1976 [2]. To our knowledge, this is the first time this combination of events has been reported and it opens up the possibility of observing similar events in other X-ray pulsars. References [1] Koliopanos F., Gilfanov M., Bildsten L., 2013, MNRAS, 432, 1264 [2] Basko M. M., Sunyaev R. A., 1976, MNRAS, 175, 395

Speaker: Dr Filippos Koliopanos (Research Institute in Astrophysics and Planetology (IRAP), Toulouse, France)

Texas_2015.pdf

16:55 Presence of a third body orbiting around XB 1916-053.

The ultra-compact dipping source XB 1916-053 has an orbital period of close to 50 min and a companion star with a very low mass (less than 0.1 M$_{\odot}$). The known orbital period derivative ($1.5(3) \times 10^{-11}$ s/s) is extremely large and can be explained by invoking an extreme, non-conservative mass transfer rate that is not easily justifiable. We extended the analysed data from 1978 to 2014, by spanning 37 years, to verify whether a larger sample of data can be fitted with a quadratic term or a different scenario has to be considered. The 27 delays associated with the dip arrival times are well fitted using a sinusoidal term plus a quadratic function or, alternatively, with a series of sinusoidal terms that can be associated with a modulation of the dip arrival times due to the presence of a third body that has an elliptical orbit. We infer that for a conservative mass transfer scenario the modulation of the delays can be explained by invoking the presence of a third body with mass between 0.10-0.14 M$_{\odot}$, orbital period around the X-ray binary system of close to 51 yr and an eccentricity of $0.28 \pm 0.15$. In a non-conservative mass transfer scenario we estimate that the fraction of matter yielded by the degenerate companion star and accreted onto the neutron star is $\beta = 0.08$, the neutron star mass is $\ge 2.2$ M$_{\odot}$, and the companion star mass is 0.028 M$_{\odot}$. In this case, we explain the sinusoidal modulation of the delays by invoking the presence of a third body with orbital period of 26 yr and mass of 0.055 M$_{\odot}$. From the analysis of the delays, we find that both in a conservative and non-conservative mass transfer scenario we have to invoke the presence of a third body to explain the observed sinusoidal modulation. We propose that XB 1916-053 forms a hierarchical triple system.

Speaker: Prof. Rosario Iaria (Univ. di Palermo - DSFC)

15_1655_Iaria_Presence_of_a_Third_body.pdf

15_1655_Iaria_Presence_of_a_Third_body.pptx

17:15 Missing hard states and regular outbursts: the puzzling case of the BHC 4U 1630–472

4U 1630–472 is a recurrent X-ray transient classified as a black hole candidate from its spectral and timing properties. One of the peculiarities of this source is the presence of regular outbursts with a recurrence period between 600 and 730 d that has been observed since the discovery of the source in 1969. We report on a comparative study, performed with INTEGRAL and RXTE, of the spectral and timing behaviour of four consecutive outbursts that occurred in 2006, 2008, 2010 and 2012. We show that, in spite of having a very similar accretion disc evolution, these four outbursts exhibit totally different characteristics of the Compton electron corona, showing a softening in their evolution rarely observed before in a low-mass X-ray binary hosting a black hole. We argue the possibility that the unknown perturbation that causes the outbursts to be equally spaced in time could be at the origin of this particular behaviour. We describe several possible scenarios that could explain the regularity of the outbursts, identifying the most plausible, such as a third body orbiting around the binary system.

Speaker: Dr Fiamma Capitanio (IAPS-INAF)

15_1715_Capitaneo_4U1630.pdf

17:35 Glitches and anti-glitches in accreting pulsars: expected properties and observability

Glitches have been observed in isolated pulsars, while a clear detection in accretion-powered X-ray pulsars is still lacking. We use the "snowplow" model for pulsar glitches of Pizzochero (2011) and starquake models to determine for the first time the expected properties of glitches in accreting pulsars. We also investigate the possibility that anti-glitches occur in accreting pulsars which show accretion-induced long-term spin-up. We find that glitches caused by quakes in a slow accreting neutron star are very rare and their detection extremely unlikely. On the contrary, glitches and anti-glitches caused by a transfer of angular momentum between the superfluid neutron vortices and the non- superfluid component may take place in accreting pulsars more often. We calculate the expected maximum jump in angular velocity of an anti-glitch and we also find that both glitches and anti-glitches in accreting pulsars are expected to have long rise and recovery time scales compared to isolated glitching pulsars. We find that, among accreting pulsars, GX 1+4 is the best candidate for the detection of glitches with currently operating X-ray satellites.

Speaker: Lorenzo Ducci (University of Tuebingen)

15_1735_Ducci_Glitches and anti-glitches.pdf

17:51 Understanding supernova kicks and black-hole spins in Galactic X-ray binaries

In recent years, an increasing number of proper motions have been measured for Galactic black hole (BH) X-ray binaries (XRBs). When supplemented with accurate determinations of the component masses and spin rates, orbital period, and donor luminosity and effective temperature, these kinematical constraints harbor a wealth of information on the systems’ past evolution. We developed an analysis that allows us to consider all this available information and reconstruct the full evolutionary history of XRBs back to the time of core collapse and compact object formation. The constraints on compact object progenitors and kicks derived from this are of immense value for understanding compact object formation and exposing common threads and fundamental differences between BH and neutron star formation. Galactic field low-mass XRBs (LMXBs), like the ones for which BH spin measurements are available, are believed to form in situ via the evolution of isolated binaries. In the standard formation channel, these systems survived a common envelope phase, after which the remaining helium core of the primary star and the subsequently formed BH are not expected to be highly spinning. However, the measured spins of BHs in LMXBs cover the whole range of spin parameters from a*~0 to a*1. In this talk I propose that the BH spin in LMXBs is acquired through accretion onto the BH during its long stable accretion phase. I find that in all Galactic LMXBs with measured BH spin, the origin of the spin can be accounted by the accreted matter. Furthermore, based on this hypothesis, I derive limits on the maximum spin that a BH can have depending on the orbital period of the binary it resides in, and give predictions on the maximum possible BH spin of Galactic LMXBs where a BH spin measurement is not yet available. Finally, I will discuss the implication that our findings have on the birth black hole mass distribution.

Speaker: Anastasios Fragkos (University of Geneva)

Fragos_TexasSymposium_December2015.pdf

18:08 Angular momentum loss by gravitational radiation in x-ray binaries with neutron stars

In this study, we present angular momentum loss mechanism through gravitational radiation for the selected system with neutron stars and gravitational radiation time-scale is estimated for them.

Speakers: Kadri Yakut (University of EGE), Tuğçe İÇLİ

proc_TIcli.pdf

18:11 gap

16:15 → 18:45 16 - Black holes

Convener: Didier Barret (IRAP (UPS/CNRS))

16:15 The Athena/X-IFU X-ray view of Hot and Energetic Universe: probing the Black Hole environment

ESA’s *Athena* (Advanced Telescope for High-Energy Astrophysics) X-ray observatory mission, to be launched in 2028, will revolutionise our knowledge of the hot and energetic Universe. The X-IFU (X-ray Integral Field Unit) is one of the two instruments on the focal plane of its large X-ray telescope, providing sensitive spatially resolved high-resolution spectroscopy. *Athena*/X-IFU will deliver: (a) 3D mapping of hot cosmic gas through spatially resolved X-ray spectroscopy; (b) Weak spectroscopic line detection and (c) Physical characterization of the hot and energetic Universe through plasma diagnostics, reverberation, line shapes, outflow/inflow spectral features etc. In combination with the other Athena instrument, the WFI (Wide Field Imager), the X-IFU will be instrumental in probing the physics around Black Holes in a range of spatial scales. In particular it will measure Super-Massive Black Hole (SMBH) spins through Fe emission line shapes and thence constrain cosmic SMBH growth models; quantify the relationship between accretion and outflows in galactic black holes and other compact sources; measure the mechanical energy of SMBH disk winds and outflows through X-ray absorption features; probe the interaction of these winds and outflows with their surroundings in local galaxies; and quantify the feedback produced by SMBH accretion on galaxy cluster scales by measuring hot gas bulk motions and turbulence.

Speaker: Xavier Barcons (Instituto de Física de Cantabria (CSIC-UC))

16_1615_Barcons_The_Athena_XIFU.pdf

16:40 How accreting black holes may shape their surroundings through AGN feedback

Black holes in active galactic nuclei (AGN) respond to the accretion process by feeding back energy and momentum into the surroundings. Such AGN feedback is generally invoked to quench star formation in host galaxies, either by heating or removing the ambient gas. However, feedback from the accreting black hole may also play other roles in galaxy evolution.We consider the role of radiation pressure on dust in driving outflows on galactic scales, and the possibility of AGN feedback triggering star formation within those feedback-driven outflows. In this picture, the accreting black hole is responsible for both driving star formation in the galaxy ("positive feedback"), as well as clearing dusty gas out of the host ("negative feedback"). I will discuss how the central black hole may shape not only the development of its own host galaxy, but also the evolution of the whole surrounding environment.

Speaker: Dr Wako Ishibashi (ETH Zurich)

Ishibashi_TexasSymposium_proc.pdf

17:00 Direct formation of supermassive black holes; from mergers of protogalaxies to global relativistic collapse

We present the latest developments of the merger-driven scenario for supermassive black hole formation originally developed in Mayer et al. (2010, Nature, 466. 1082). We show how including realistic radiation physics in mergers of protogalaxies driven from cosmological initial conditions strengthens the proposal that supermassive nuclear clouds may form in only a few 10^8 yr in the nucleus of the remnant, as a result of supersonic turbulence hampering fragmentation and normal star formation even in the presence of metal-enriched gas. The billion solar mass clouds can lead to a supermassive star, which can rapidly produce a massive black hole seed (M_BH > 10^5 Mo), or can undergo a "dark collapse" all the way into a supermassive black hole via the relativistic radial instability depending on the residual angular momentum (Mayer et al. 2015, ApJ, in press). Both scenarios explain naturally the rapid emergence of high-z QSOs at z > 6. Finally, unprecedented 3D computations joining for the first time galaxy formation simulations in a cosmological context with relativistic hydro calculations of supermassive cloud collapse, including even the effect of nuclear burning in metal-enriched gas, will be presented and the preliminary results discussed in light of the "dark collapse" scenario.

Speaker: Prof. Lucio Mayer (University of Zurich)

16_1700_Mayer_Direct formation of supermassive black holes; from mergers of protogalaxies to global relativistic collapse.key

16_1700_Mayer_Direct formation of supermassive black holes; from mergers of protogalaxies to global relativistic collapse.pdf

17:20 Cosmological mass transport on galactic nuclei and the formation of high redshift quasars.

By using AMR cosmological hydrodynamic N-body zoom-in simulations, with the RAMSES code, we studied the mass transport processes onto galactic nuclei from high redshift up to z~6. Due to the large dynamical range of the simulations we were able to study the mass accretion process on scales from ~50 kpc to ~pc. The SMBHs are modelled as a sink particles at the center of our galaxies, which allowed us to quantify the BH growth in relation with the mass transport processes associated to three different angular momentum fluxes: i) Reynolds stress, ii) gravitational stress and iii) viscous stress. Such a quantification allowed us to identify the main mass transport process as a function of the scales of the problem. We found that in simulations that include radiative cooling and SNe feedback, the SMBH grows at the Eddington limit most of the time. The disk momentum flux is dominated by the Reynolds stress transporting mass at a rate of ~1-10 Msun/yr. This level of SMBHs accretion rates found in our cosmological simulation, are needed in all models of SMBH growth attempted to explain the formation of redshift 6-7 quasars.

Speaker: Prof. andres escala (Universidad de chile)

16_1720_Escala_Cosmological_Mass_Transport.ppt

Sne005.mov

Sne005Temp.mov

17:40 Does the obscured AGN fraction really depend on luminosity?

We have utilized a local AGN sample from the INTEGRAL all-sky hard X-ray survey to investigate if the well-known declining trend of the fraction of obscured AGN with increasing luminosity is mostly an intrinsic or selection effect. We show that in addition to negative bias, due to absorption in the torus, in finding obscured AGN, there is positive bias in finding unobscured AGN, due to Compton reflection in the torus. These biases lead to a decreasing observed fraction of obscured AGN with increasing luminosity even if this fraction has no intrinsic luminosity dependence, this effect being stronger if there is intrinsic collimation of hard X-ray emission along the axis of the torus. We conclude that if the central AGN source is isotropic, the intrinsic obscured AGN fraction does decrease with increasing luminosity, although this fraction is higher than thought before: >85% at L<10^42.5 erg/s and <60% at L>10^44 erg/s (17-60 keV), which implies that the torus half-opening angle is <30 deg and >45 deg, respectively. If, however, the emission from the central SMBH is moderately collimated, the intrinsic obscured AGN fraction is consistent with a luminosity-independent torus half-opening angle of ~30 deg. MNRAS (in press), arXiv:1509.01259

Speaker: Dr Sergey Sazonov (Space Research Institute, Moscow, Russia)

Obscured_AGN_Dec2015.pdf

18:00 Mildly obscured active galaxies and the diffuse X-ray background

The diffuse cosmic X-ray background1 (CXB) is the sum of the emission of discrete sources, mostly massive black-holes accreting matter in active galactic nuclei (AGN)2. The CXB spectrum differs from the integration of the spectra of individual sources, calling for a large population, undetected so far, of strongly obscured Compton thick AGN3. Such objects are predicted by unified models4, which attribute most of the AGN diversity to their inclination on the line of sight, and play an important role for the understanding of the growth of black holes5 in the early Universe. The fraction of obscured AGN at low redshift can be derived from the observed CXB spectrum assuming AGN spectral templates and luminosity functions. Here we show that high signal-to-noise average hard X-ray spectra, derived from more than a billion seconds of effective exposure with the Swift/BAT instrument6, imply that mildly obscured Compton thin AGN feature a strong reflection and contribute massively to the CXB. A population of Compton thick AGN larger than that effectively observed is not required, as no more than 8% of the CXB flux can be attributed to them. Stronger reflection in mildly obscured AGN suggests that the covering fraction of the gas and dust surrounding their central engines is a key factor in shaping their appearance. These mildly obscured AGN are easier to study at high redshift than Compton thick sources.

Speaker: Valentino Esposito

16_1800_Esposito_mildly_obscured_and_cxb.pdf

18:20 Disentangling AGN and Star Formation Contributions in the Central Parsec of NGC 4945

NGC 4945, one of the closest starburst-AGN presents a unique laboratory for testing the interplay between AGN accretion and star formation. It is the brightest extragalactic source of hard X-rays but is highly obscured below 10 keV. Its proximity allows for mapping the inner-most parsec of the galactic nucleus using very long baseline interferometry of the unobscured 22 GHz water maser emission. Combining the sub-parsec scale maser map with X-ray and infrared images of larger scale structures allows for the disentangling of contributions from the AGN and star formation. In this system, the masers are found in the thick, clumpy, circumnuclear disk as well as the shocks that trace the base of the X-ray and infrared wind. The masers pinpoint the location of the supermassive black hole and provide evidence that the wind is driven by the AGN rather than the star formation. Furthermore, some of the maser emission in the disk does not follow Keplerian rotation, indicating fragmentation and star formation in the sub-parsec scale disk.

Speaker: Ingyin Zaw (NYU Abu Dhabi)

Texas_PosterPres_NGC4945.key

Texas_PosterPres_NGC4945.pdf

18:23 An eclipsing binary black hole in MRK 421

A model independent power spectrum light curve analysis in the optical, hard X-ray and gamma-rays of the blazar MRK 421 shows clear evidence for a periodicity of approximately 400 days. A subsequent full maximum likelihood analysis fitting an eclipse model confirms this periodicity with a consistent phase for the bands analysed. The most parsimonious physical mechanism to which this periodicity could be ascribed is a dynamical effect produced by an orbiting supermassive black hole companion of mass of about 10^7 solar masses eclipsing the central black hole, which has an approximate mass of 10^8 solar masses.

Speakers: Dr Erika Benitez (Instituto de Astronomia, Universidad Nacional Autonoma de Mexico (UNAM)), Dr Sergio Mendoza (Instituto de Astronomia, Universidad Nacional Autonoma de Mexico)

16_1823_Mendoza_Eclipsing_binary.pdf

mendoza_benitez-texas2015.pdf

18:26 The high energy spectrum of 3C 273

The high energy spectrum of 3C 273 is usually understood in terms of inverse-Compton emission in a relativistic leptonic jet. This model predicts variability patterns and delays that could be tested with simultaneous observations from the radio to the GeV range. The instruments IBIS, SPI, JEM-X on board INTEGRAL, PCA on board RXTE, and LAT on board Fermi have enough sensitivity to follow the spectral variability of 3C 273 from the keV to the GeV. We looked for correlations between the different energy bands, including radio data at 37 GHz collected at the Metsähovi Radio Observatory and built quasi-simultaneous multiwavelength spectra in the high energy domain when the source is flaring either in the X-rays or in the γ rays. Both temporal and spectral analysis suggest a two-component model to explain the complete high energy spectrum. X-ray emission is likely dominated by a Seyfert-like component while the γ-ray emission is dominated by a blazar-like component produced by the relativistic jet. The variability of the blazar-like component is discussed, comparing the spectral parameters in the two different spectral states. Changes of the electron Lorentz factor are found to be the most likely source of the observed variability.

Speaker: Valentino Esposito

16_1826_Esposito_the_high_energy_spectrum_3C273_talk.pdf

16_Esposito_the_high_energy_spectrum_3C273_poster.pdf

18:29 gap

16:15 → 18:45 18 - Gal. accel. & pulsars: Pulsars

Convener: Marco Tavani (INAF)

16:15 Progress on the knowledge of magnetic fields in neutron stars

With about 300 refereed papers published each year, XMM-Newton is one of the most successful scientific missions of ESA ever. Neutron stars are classical targets of X-ray observatories and consequently huge expectations were accompanying the lunch of the spacecraft. Contrary to expectations, the spectra of neutron stars were generally found continuum dominated exclusive any spectral features. The situation has dramatically changed during the last years as variable spectral features were detected for several neutron stars and magnetars. These findings allow unique view of the different magnetic field components of neutron stars. In the talk I will illustrate the achieved progress with selected highlights of XMM-Newton observation of neutron stars.

Speaker: Norbert Schartel (ESA)

18_1615_Schartel_Progress_on_the_knowledge.pdf

18_1615_Schartel_Progress_on_the_knowledge.ppt

SpinningPulsar_07_400p.wmv

16:35 General-relativistic pulsars magnetospheres

Pulsar magnetospheres are shaped by ultra-relativistic electron/positron plasmas flowing in a strong magnetic field and subject to strong gravitational fields. The former induces magnetospheric currents and space charges responsible for the distortion of the electromagnetic field based on pure electrodynamics. The latter induces other perturbations in these fields based on space-time curvature. The force-free approximation describes the response of this magnetosphere to the presence of currents and charges and has been investigated by many authors. In this context, general relativity has been less discussed to quantify its influence on the neutron star electrodynamics. It is the purpose of this paper to compute general-relativistic force-free pulsar magnetospheres for realistic magnetic field configurations such as the inclined dipole. We performed time-dependent simulations of Maxwell equations in the 3+1 formalism of a stationary background metric in the slow-rotation approximation. We computed the resulting Poynting flux depending on the ratio R/rL and on frame-dragging through the spin parameter as. Both effects act together to increase the total Poynting flux seen by a distant observer by a factor of a few. Moreover we retrieve the sin^2 chi dependence of this luminosity, chi being the obliquity of the pulsar, as well as a braking index close to n=3.

Speaker: Jérôme Pétri (Université de Strasbourg)

18_1635_Petri_General_relativistic_pulsar_magnetospheres.pdf

16:55 Relativistic pulsar winds: structure, shocks, reconnection.

Using the latest multi-wavelength observations of the inner-most regions of Crab nebular, we develop a model of relativistic pulsar winds that reproduces the detailed morphology of the Crab inner knot. We infer that a large equatorial sector of the wind, responsible for the production of the inner knot, is a low-magnetized flow - we see directly the surface of the termination shock. At intermediate polar angles the wind is highly magnetized. Using analytical and numerical approaches we develop a model of explosive reconnection events in relativistic highly magnetized post-shock plasma, and apply the model to explain the Crab gamma-ray flares. Flares are produced during explosive merger of macroscopic current-carrying magnetic flux tubes. During the merger small relative number of particles are accelerated to energies well above the average magnetic energy per particle.

Speaker: Maxim Lyutikov

18_1655_Yutikov_PICsar.key.zip

18_1655_Yutikov_PICsar.pdf

17:15 PICsar: Particle in Cell Pulsar Simulations

We perform 2.5D axisymmetric simulations of the pulsar magnetosphere (aligned dipole rotator) using the charge conservative, relativistic, electromagnetic particle in cell code PICsar. The particle in cell method is a powerful tool for studying the pulsar magnetosphere, because it can handle the force-free and vacuum limits as well as magnetic reconnection. In particular, dissipative regions in the solution arise self-consistently, since we do not have any explicit dissipation in the code. The structure of the electromagnetic fields in our simulations is on the whole consistent with the force-free model, and the value of the spin-down luminosity is within ≈10% of the force-free value. However, a minimum of ≈15-20% (and as high as 50% depending on the plasma density at the light cylinder) of the electromagnetic spin-down luminosity is transferred to the particles within five light cylinder radii. The energy is transferred to the particles most efficiently near the Y-point and could potentially be radiated in the form of gamma rays. In the future, PIC codes could be used to better constrain the sites of gamma ray emission in the pulsar magnetosphere.

Speaker: Mikhail Belyaev (UC Berkeley/TAC)

picsar_texas2015.key

picsar_texas2015.pdf

17:35 Effect of geodetic precession on the evolution of pulsar high-energy pulse profiles as derived with the striped-wind model.

Geodetic precession has been observed directly in the double-pulsar PSR J0737-3039. Its rate has even been measured and agrees with predictions of general relativity. Very recently, the double pulsar has been detected in X-rays and gamma-rays. This fuels the hope observing geodetic precession in its high-energy pulse profile. Unfortunately, the geometric configuration of the binary renders any detection of such an effect unlikely. Nevertheless, this precession is present in other relativistic binaries or double neutron star systems containing at least one X-ray or gamma-ray pulsar. We compute the variation of the high-energy pulse profile expected from this geodetic motion according to the striped-wind model. We compare our results with two-pole caustic and outer gap emission patterns. For a sufficient misalignment between the orbital angular momentum and the spin angular momentum, a significant change in the pulse profile as a result of geodetic precession is expected in X-rays and gamma-rays. The essential features of the striped wind is summarized in several plots showing the evolution of the maximum of the pulsed intensity, the separation of both peaks, if present, and the variation in the width of each peak. We highlight the main differences with other competing high-energy models. Some predictions about possible future detection of high-energy emission from double neutron star systems with the highest spin precession rate are made. Such observations will definitely favor some pulsed high-energy emission scenarios.

Speaker: Jérôme Pétri (Université de Strasbourg)

18_1735_Petri_Effect_of?Geodetic_Precession.pdf

17:55 The Crab pulsar: Examining its profile and deriving high precision X-ray ephemerides

We present here the results of an analysis of 15 years of regular XMM-Newton EPIC pn observations of the Crab pulsar. The analysis of its pulse profile is based on a multi-harmonic decomposition using a new periodogram statistic which is ideally suited for studying the details of the characteristics of peaked pulse profiles such as the Crab’s, especially in time-tagged event data. The decomposition and generalised modified Rayleigh statistic are both applied and presented here for the first time. Their application is extended to study the time-dependent evolution of the pulsar’s emission over this 15 year period and 70 individual observations to derive high precision ephemerides based solely on the X-ray data.

Speaker: Guillaume Belanger (ESA)

18_1755_Belanger_Crab_pulsar.pdf

17:58 gap

16:15 → 18:45 10 - Cosmic magnetic fields: Probes

Convener: Tina Kahniashvili

16:15 Constraints on Primordial Magnetic Fields from Planck 2015

Primordial magnetic fields (PMF) may represent the "progenitors" of the fields we observe in large scale structures and their study could open a new observational window on the early universe. The Cosmic Microwave Background, thanks to its different probes, represents one of the best laboratory to investigate and constrain the nature of PMF. I will present the Planck 2015 constraints on the amplitude and spectral index of a stochastic background of PMF derived using different methods.

Speaker: Daniela Paoletti (INAF and INFN)

Paoletti_PMFPlanck2015_Proceedings_Texas.pdf

Paoletti_Primordial_Magnetic_Fields_Texas_2.pdf

16:35 Prospects of constraining primordial magnetic fields using their effects on CMB, LSS and ionization history

The presence of large scale magnetic fields at different epochs can be probed by their impact on different observables such as the CMB spectrum, primary and secondary CMB anisotropies, matter power spectrum and 21cm line emission. I will give an overview of these effects together with constraints from current and future experiments.

Speaker: Dr Kerstin Kunze (University of Salamanca)

10_1635_Kunze_Prospect_of_constraining.pdf

16:55 Primordial Magnetism in CMB

I will discuss CMB signatures of primordial magnetic fields, some of the existing constraints, and what can be expected from future CMB experiments.

Speaker: Dr Levon Pogosian (Simon Fraser University)

Pogosian_Dec15.pdf

17:15 Parity odd CMB power spectrum via helical magnetic field.

In this work we compute the temperature-polarization correlations (C_l^(TB) and C_l^(EB)) in the cosmic microwave background (CMB) generated by the presence of causal primordial magnetic fields with a helical contribution. We analize the effect of an infrared cutoff in the power spectrum of causal fields on the cross-correlation and we compare our result with previous work.

Speaker: Hector Javier Hortua (Universidad Nacional)

poster-texas.pdf

proc-Hortua.pdf

17:18 gap

16:15 → 18:45 09 - Cosmic neutrinos

Convener: Julien Lesgourgues

16:15 Constraining non-standard neutrino scenarios with Planck 2015

Cosmological observations represent a powerful tool to constrain neutrino physics. In particular, observations of the temperature and polarization anisotropies of the cosmic microwave background (CMB) have the potential to constrain the properties of relic neutrinos, and possibly of additional light relic particles in the Universe. Even if all current cosmological data are well in agreement with the standard scenario of just three active neutrinos with negligible masses, interacting only through the weak force, and having an equilibrium spectrum with vanishing chemical potential, nevertheless deviations from this simple scenario are possible. For example, “hidden” (i.e. beyond the standard model of particle physics) neutrino interactions, mediated by a scalar particle like the Majoron, could exist and affect the evolution of cosmic relic neutrinos. Another possibility is that neutrinos do not have an equilibrium distribution, like e.g. in scenarios with a low reheating temperature. In my talk I will discuss constraints on these deviations from the standard scenario that can be obtained using the recently released data from the Planck satellite, possibly in combination with other astrophysical and cosmological probes.

Speaker: Massimiliano Lattanzi (University of Ferrara)

09_1615_Lattanzi_Constraining_non_standard.pdf

16:36 Sterile neutrinos with secret interactions

The motivation for new non-standard interactions in the sterile neutrino sector arises from the tension between oscillation data and cosmological data, indeed the former point towards the existence of one (or more) light sterile neutrino in the eV mass range, while the latter disfavor additional massive species with high statistical significance. However a partial thermalization induced by secret interactions can solve this tension, making eV sterile neutrinos fully consistent with big bang nucleosynthesis, cosmic microwave background and large scale structure measurements. In this talk I will present a pseudoscalar model of secret interactions which provides a simple and elegant way of reconciling eV sterile neutrinos with precision cosmology. I will also mention how the hidden interactions can be extended to the dark matter sector and might mitigate the small scale problems of the standard cold dark matter paradigm.

Speaker: Maria Archidiacono

TEXAS_archidiacono_p.pdf

16:57 Constraining sterile neutrinos with lyman alpha forest

We reconsider the problem of determining the warmness of dark matter from the growth of large scale structures. In particular, we have re-analyzed the previous work of Viel et al 2013, based on high resolution Lyman-alpha forest spectra. In fact, the flux power spectrum exhibits a cut-off below ~ 1.5 Mpc/h, this may be explained by the temperature of the intergalactic medium (IGM) or be due to the free-streaming of dark matter particles. We show that if the IGM temperature at high redshifts was low enough (rising at later times) then the data indeed prefer warm dark matter. Assuming this broader range of thermal histories, we find that mWDM >= 2.1 keV for thermal relic at 95% CL (mNRP >= 12 keV for non-resonantly produced sterile neutrino). We discuss an independent method that would allow to exclude the influence of WDM on observable small-scale structures, or would lead to the discovery of WDM. We also determine values of lepton asymmetry making resonantly produced 7 keV sterile neutrinos consistent with the data.

Speaker: Dr Antonella Garzilli (Leiden University)

proceeding.pdf

talk.key.zip

talk.pdf

17:18 A loophole to the electromagnetic cascade theory : Solving the lithium problem with a sterile neutrino.

After a recap of the standard e.m. cascade theory, I will discuss a loophole that can have a large effect in the early universe, notably in altering primordial nucleosynthesis bounds on electromagnetically decaying relic particles. I will finally show how this may greatly simplify the possibility to address the long-standing "lithium problem" in terms of new physics models, and solve it explicitely with a proof-of-principle particle physics model, namely the sterile neutrino.

Speaker: Vivian Poulin (Unite Reseaux du CNRS (FR))

Lithium_Symposium_VivianPoulin.pdf

proceeding_Lithium_Vivian_Poulin.pdf

17:39 The effective number of neutrinos: standard and non-standard calculations

We have performed a new numerical calculation of the decoupling process of neutrinos in the early Universe, including the values of all mixing parameters from a recent analysis, taking into account the full set of differential equations for the neutrino density matrices (equivalent to the occupation numbers for mixed neutrinos). Our results are important for fixing the radiation content of the Universe in the standard case in terms of Neff, recently measured by Planck. We also show to which extent the value of Neff can be enhanced in the presence of non-standard neutrino interactions with electrons, and we have also considered the case of a very low reheating scenario, where the last radiation-dominated phase of the Universe begins at temperatures as low as MeV. The main consequence of such scenarios concerns the production of neutrinos, because they are the known relativistic particles with the largest decoupling temperature. The thermalization of the neutrino background could be incomplete due to the lack of interactions, leading to Neff < 3. We will show the bounds on the reheating temperature both from BBN and from late-time cosmological observables, including the latest results of the Planck satellite.

Speaker: Pablo Fernández de Salas (IFIC - CSIC/Universidad de Valencia)

TEXAS-Neff-Slides.pdf

18:00 Higher-order massive neutrino perturbations in large-scale structure

I will present a new first principle approach for higher order perturbation theory for hot and warm dark matter in large scale structure. The approach is based on a non-linear generalization of Gilbert's equation. Combined with standard perturbation theory, it allows to calculate N-point statistics of density perturbations in mixed cold+hot dark matter cosmologies. I apply the theory to compute the leading order bispectrum in a mixed CDM+neutrino universe and use it as benchmark to test the validity of some simple approximations schemes

Speaker: Florian Führer (Institut für Theoretische Physik, Universität Heidelberg)

higher_order_neutrinos_LSS_fuehrer.pdf

18:20 Neutrinos beyond the linear regime: a new theoretical approach

There is now no doubt that neutrinos are massive particles fully involved in the nonlinear growth of the large-scale structure of the universe. A problem is that their nonlinear behavior is particularly difficult to describe by theoretical models. In my talk, I will present a new method allowing to deal with massive neutrinos beyond the linear regime. The key idea is to describe neutrinos as a collection of flows instead of considering them as a single multi-flow fluid. In this framework, no velocity dispersion has to be taken into account and the time evolution of neutrinos can be encoded in fluid equations similar to the ones describing cold dark matter. Hopefully, this approach is a further step towards a computation of the nonlinear matter power spectrum in the presence of massive neutrinos.

Speaker: Hélène DUPUY

Dupuy.pdf

18:40 Decoherence of cosmological massive neutrinos

The transition of cosmological massive neutrinos into the non-relativistic regime acts as a decoherence process which also changes the oscillation probability, reaching different values for the asymptotic flavour composition. Furthermore, this effect could also increase the entropy inside the neutrino ensemble, triggering the formation of bulk viscosity and introducing fluctuations in the gravitational potential, which in turn induces secondary anisotropies in the cosmic microwave background by the integrated Sachs-Wolfe effect.

Speaker: Daniel Boriero

09_1842_Daniel_Neutrino_cosmic_viscosity.pdf

18:43 Joint constraints on neutrino mass and number of effective neutrino species from cosmology

We present joint constraints on the number of effective neutrino species Neff and the sum of neutrino masses, using a technique based on state-of-the-art hydrodynamical simulations with massive neutrinos, which allows one to exploit the full information contained in the one-dimensional Lyman-Alpha forest flux power spectrum complemented by additional cosmological probes. Our results provide strong evidence for the cosmic neutrino background (Neff = 0 is rejected at more than 14σ), and rule out the possibility of a sterile neutrino thermalized with active neutrinos at a significance of over 5σ – one of the strongest bounds to date.

Speaker: Graziano Rossi (Sejong University)

neff_poster_talk_rossi.pdf

proceeding_graziano_rossi_texas_2015.pdf

16:15 → 18:45 19 - VHE & CR: Blazars and EBL

Convener: Elisa Prandini (University of Geneva)

16:35 FACT: Monitoring TeV Blazars with Silicon Photomultipliers

The First G-APD Cherenkov Telescope (FACT) has pioneered the use of solid state photosensors (G-APD/SiPM) in astroparticle physics. Data-taking started in October 2011, and the system has operated remotely for over three years. G-APDs have proven to be very reliable and have enabled FACT to produce the first Crab nebulae spectra from such an instrument and collect large unbiased data sets on extra-galactic blazars, including Mrk 501 and Mrk 421. These two objects are close-by and highly variable, providing us with an excellent opportunity to study this source class. This presentation will describe the status of FACT and report the lessons learned regarding the usage of SiPM in Cherenkov telescopes. Contemporaneous correlations between FACT and measurements in other wavelengths will be shown, along with preliminary searches for quasi-periodic modulation. We will also present potential future extensions to this technology that would enable the constant monitoring of these sources.

Speaker: Gareth Hughes (ETH Zurich)

FACT_Texas_hughes_v5.pdf

16:55 MWL characterization of the blazar S5 0716+714 by MAGIC during its brightest outburst

S5 0716+714 is a well known BL-Lac object, located at a redshift of z=0.31. The discovery in the Very High Energy band (VHE, E> 100 GeV) by MAGIC happened in 2008, when Fermi data in the High Energy (HE, 100 MeV < HE<100 GeV) were not yet available. In January 2015 the source went through the brightest optical state ever observed, triggering MAGIC follow-up and a VHE detection with ~13 sigma significance (Atel #6999). The availability of simultaneous Fermi-LAT observations allows to constrain the Inverse Compton peak of the spectrum. We will present the preliminary analysis of MAGIC data of the flaring activity in January and February 2015 and discuss the time variability of the spectrum in VHE during this impressive outburst. Multi Wave Length data including the mm/optical/X-ray/HE bands will be reported. Preliminary study on the Extragalactic Background Light absorption will also be shown, with implications on current EBL models.

Speaker: Dr Marina Manganaro (IAC)

Texas_Symposium_S50716_pub.pdf

17:15 The first detection of the blazar S4 0954+65 at very-high energies with the MAGIC Telescopes during an exceptionally high optical state

The blazar S4 0954+65 (at a redshift of z=0.368) underwent an exceptionally high state in optical during January and February 2015, as revealed by the Tuorla and St.Petersburg University blazar monitoring programs: a brightening of more than 3 magnitudes in the R-band from the average monitored states. Simultaneous data from the Fermi-LAT satellite at high energy gamma rays (100MeV < E < 100GeV) also show a period of increased activity. MAGIC observations, triggered by these enhanced emissions in lower energy bands, led to the discovery of very high energy (VHE, E>100 GeV) emission from S4 0954+65 (ATel #7080). The VHE flux above 150GeV is estimated to be about 6% of the Crab nebula flux above the same threshold. In this contribution we present a comprehensive multiwavelength picture of this object, including data from mm/optical/X-ray/HE and VHE gamma-ray bands along with analysis of the parsec scale jet behavior.

Speaker: Giovanna Pedaletti (DESY)

s40954plus65_gp_texas15_last.pdf

17:35 Flat spectrum radio quasars at very high energies: the new detection of PKS 1441+25

The detection of Flat Spectrum Radio Quasars (FSRQs) in the Very High Energy (VHE, E$>$100 GeV) range is challenging, mainly due to their steep soft spectra in this energy band. Thus far, only five FSRQs are known to be VHE gamma-ray emitters, all of which have been detected by the MAGIC telescopes, which made the first VHE detection of four of them. Observations in the VHE band are crucial to understand their emission, especially to constrain the location of the emitting region within the jet due to the absorption from their broad line region (BLR). The most recent member of the VHE FSRQ family is PKS 1441+25 (z=0.940) which was detected in this band for the first time by the MAGIC telescopes on April 2015. The observations were triggered by the flaring activity detected by the Fermi-LAT at High Energies (HE, 100 MeV < E < 100 GeV). Aside from the gravitationally lensed VHE blazar QSO B0218+357 (z = 0.944), also detected by MAGIC, PKS 1441+25 is the most distant VHE blazar observed to date. For the first time, the VHE gamma-ray spectrum was used to indirectly probe the extragalactic background light at redshifts out to z ~ 0.94 from sensitive ground Cherenkov observations in the energy range from 40 to 250 GeV. In this contribution we will review the last results on the observations of VHE FSRQs with the MAGIC telescopes in a multi-wavelength context with special focus on the new detection of PKS 1441+25.

Speaker: Josefa Becerra Gonzalez (NASA GSFC)

VHE_FSRQs_jbecerra_Texas2015.pdf

17:55 Evidence for quasi-periodic modulation in the gamma-ray blazar PG 1553+113

For the first time a gamma-ray and multiwavelength nearly-periodic oscillation in an active galactic nucleus is reported using the Fermi Large Area Telescope (LAT). A quasi-periodicity in the gamma-ray flux (E>100 MeV and E>1 GeV) is observed from the well-known GeV/TeV BL Lac object PG 1553+113 (Ackermann et al. submitted). The significance of the 2.18 +/- 0.08 year-period gamma-ray modulation, seen in 3.5 oscillation maxima observed, is supported by significant cross-correlated variations observed in radio and optical flux light curves, through data collected in the OVRO, Tuorla, KAIT, and CSS monitoring programs and Swift UVOT. The optical cycle, appearing in about 10 years of data, has a similar period, while the radio-band oscillation observed at 15 GHz is less regular and coherent. The available X-ray flux data obtained by Swift XRT appears also to be linearly correlated with the gamma-ray flux. Further long-term multi-wavelength monitoring of this blazar may discriminate among the possible explanations for this first evidence of periodicity. In this view a multi-wavelength campaign, from radio to VHE gamma rays was started in 2015 (Hughes et al. this conference).

Speaker: Antonio Stamerra (INAF-OATo / SNS-Pisa)

PG1553Periodicity_TexasSymposiumDec2015_Stamerra.pdf

18:15 Multi-wavelength observations on the gamma-ray periodic blazar PG1553+113

PG 1553+113 is a blazar with an uncertain redshift detected at very high energies (VHE; E > 100 GeV) both during high and quiescent flux states. The Fermi/LAT collaboration recently reported the detection of a ~2-year modulation of the integral flux emitted in both optical and high-energy (HE) gamma rays(Stamerra et al. at this conference). Interestingly, one of the physical scenarios that can account for such variability pattern is the presence of a supermassive black hole binary in the nucleus of PG 1553+113. The MAGIC telescopes have observed PG 1553+113 at VHE since 2005. An intense multi-wavelength campaign aimed at unbiased monitoring of the source activity, from radio to VHE gamma rays, started in 2015. Here we will show the multiwavelength data going back almost a decade, from radio to VHE, along with the results from the ongoing observations.

Speaker: Gareth Hughes (ETH Zurich)

19_1815_HUGHES_multiwavelength-observation.pdf

18:35 The long-term optical study of VHE blazars

To study optical variability of extragalactic objects, namely VHE blazars, we are conducting in Abastumani Observatory since 1997 a long-term campaign using dedicated telescopes, which allowed to collect ~300 000 CCD frames during 2 800 nights. This extensive monitoring campaign over 100 blazars during five years was carried out in BVRI bands and later on from 2002 mainly in R band using the 70-cm meniscus (f/3, SBIG ST6 and Apogee Ap6E), 125-cm Ritchey-Chretien (f/13, Apogee Ap6E) and Calar-Alto Observatory (123-cm and 220-cm) telescopes. Most densely sampled sources are 1ES 0229+200, 1ES 0806+524, 1ES 1011+496, Mrk 421 Mrk 501, 1ES 1221+302, Pg 1553+113, 1ES 1959+650, 1ES 2344+514 and others. The frames have been reduced using Daophot II and homogenous sample of lightcurves have been constructed. The amplitudes of long-term variability are within 0.3-1.5 magnitudes. Few sources show Intra-day variability within 0.05-0.15 magnitudes, while intra-night/micro-variability is below 0.05 magnitudes. The results of multiwavelength campaigns with Whipple, VERITAS, HESS and MAGIC are also presented. To extend in the future optical photometric, polarimetric and spectral survey of fainter sources with high temporal resolution, we are considering purchase of two PanSTAR like telescopes.

Speaker: Omar Kurtanidze (Abastumani Observatory)

18:38 gap

16:15 → 18:45 03 - Modifications of gravity

Convener: Anne-Christine Davis (Cambridge University)

16:15 The radial velocity profile of the filament galaxies in the vicinity of the Virgo cluster as a test of gravity

The radial velocities of the galaxies in the vicinity of a massive cluster shows deviation from the pure Hubble flow due to their gravitational interaction with the cluster. According to a recent study of Falco et al. with a high-resolution N-body simulation based on General Relativity (GR), the radial velocity profile of the galaxies located at distances larger than three times the virial radius of a neighbour cluster has a universal shape and could be reconstructed from direct observables provided that the galaxies are distributed along one dimensional filament. Analyzing the narrow filamentary structure identified by Kim et al. in the vicinity of the Virgo cluster from the NASA-Sloan-Atlas catalog, we reconstruct the radial velocity profile of the Virgo filament galaxies and compare it with the universal formula derived by Falco et al. It is found that unless the virial mass of the Virgo cluster exceeds 1015h−1M⊙ the universal formula fails to describe the reconstructed radial velocity profile whose peculiar velocity term turns out to decrease much less rapidly. Speculating that the disagreement between the GR prediction and the observed radial velocity profile of the Virgo filament galaxies may be due to the presence of unscreened fifth force, we suggest the radial velocity profile of the filament galaxies around the clusters as a powerful test of gravity on the cosmological scale.

Speaker: Prof. Jounghun Lee (Seoul National University)

16:35 A Universal velocity dispersion profile for pressure supported systems: evidence for MONDian gravity across 12 orders of magnitude in mass

For any MONDian extended theory of gravity where the rotation curves of spiral galaxies are explained through a change in physics rather than the hypothesis of dark matter, a generic dynamical behaviour is expected for pressure supported systems: an outer flattening of the velocity dispersion profile occurring at a characteristic radius, where both the amplitude of this flat velocity dispersion and the radius at which it appears are predicted to show distinct scalings with the total mass of the system. By carefully analysing dynamics of globular clusters, elliptical galaxies and galaxy clusters, we are able to significantly extend the astronomical scales over which MONDian gravity has been tested, from those of spiral galaxies, to the much larger range covered by pressure supported systems. We show that a universal projected velocity dispersion profile accurately describes various classes of pressure supported systems, and further, that the expectations of extended gravity are met, across twelve orders in magnitude in mass. These observed scalings are not expected under dark matter cosmology, and would require particular explanations tuned at the scales of each distinct astrophysical system.

Speaker: Mr Reginaldo Durazo (Instituto de Astronomía, Universidad Nacional Autónoma de México)

16:55 Searching for new short-range forces using optically levitated microspheres

We are developing a novel technique to search for non-Newtonian gravitational forces at micron length scales using optically levitated dielectric microspheres. At high vacuum, dissipation of the microsphere's motion due to residual gas collisions becomes small, allowing sub-attonewton force sensitivity. As a first demonstration of the ability to perform sensitive force measurements with these techniques, we have searched for the presence of stable, millicharged particles bound in the microspheres. These techniques can also enable searches for screened scalar particles, such as the chameleon, which have been proposed to account for dark energy at cosmological distances, but which would also lead to detectable forces at distances below 100 $\mu$m. We will describe the experimental apparatus, the results from the search for millicharged particles, and the expected sensitivity of a search for non-Newtonian forces at micron length scales.

Speaker: David Moore (Stanford University)

20151215_texas_symp.pdf

17:25 The variation of the fine-structure constant from disformal couplings

We study a theory in which the electromagnetic field is disformally coupled to a scalar field, in addition to a usual non--minimal electromagnetic coupling. We show that disformal couplings modify the expression for the fine--structure constant, $\alpha$. As a result, the theory we consider can explain the non--zero reported variation in the evolution of $\alpha$ by purely considering disformal couplings. We also find that if matter and photons are coupled in the same way to the scalar field, disformal couplings itself do not lead to a variation of the fine--structure constant. A number of scenarios are discussed consistent with astrophysical, geochemical, laboratory and the cosmic microwave background radiation constraints on the cosmic evolution of $\alpha$. We also use cosmological data, including type Ia supernova data for which we present an effective dark energy equation of state. We find that the Oklo bound in particular will put strong constraints on the model parameters. From our numerical results, we find that the introduction of a non--minimal electromagnetic coupling enhances the cosmological variation in $\alpha$. Better constrained data is expected to be reported by ALMA and with the forthcoming generation of high--resolution ultra--stable spectrographs such as PEPSI, ESPRESSO, and ELT--HIRES. Furthermore, an expected increase in the sensitivity of molecular and nuclear clocks will put a more stringent constraint on the theory.

Speaker: Mr Jurgen Mifsud (Consortium for Fundamental Physics, School of Mathematics and Statistics, University of Sheffield)

presentation.pdf

17:45 Lorentz violation in gravity

After briefly explaining why Lorentz violating theories of gravity are interesting for quantum gravity, I will discuss how they can be tested with current astrophysical and cosmological observations.

Speaker: Diego Blas Temino (CERN)

15TexasBlasII.pdf

18:10 Is the Ni's solution of the Tolman-Oppenheimer-Volkoff problem without the maximum-mass limit applicable to the real neutron stars? A discussion

In 2011, Jun Ni published solution of the equations in the classical Tolman-Oppenheimer-Volkoff (TOV) modeling of spherically symmetric neutron star. The Ni's solution implies no upper-mass limit and the outer surface of modeled object always appears to be above the event horizon. In fact, Ni found an infinite variety of sets of the TOV-problem solutions. The original Oppenheimer-Volkoff result provides only a single set from this variety offered by general relativity. As originally Openheimer and Volkoff as Ni assumed the positive energy density and pressure (or zero in the vacuum outside the object). And, the gravity of every mass element of the object had the attractive character. Ni noted that this type of solution cannot be obtained in Newtonian physics. However, general relativity may not obey the limitations sourcing from the Newtonian gravity and, thus, it seems that the neutron-star models based on the Ni's solution are still applicable on real compact objets. We discuss the relevance of main objections against this applicability.

Speaker: Dr Lubos Neslusan (Astronomical Institute, Slovak Academy of Sciences, 05960 Tatranska Lomnica, Slovakia)

posterNESLUSAN.pdf

procNESLUSAN.pdf

18:13 A relativistic metric extension of gravity based in the dynamics and lensing of individual, groups and clusters of galaxies

A metric extension of gravity based on the Tully-Fisher law is presented. It will be shown that the Tully-Fisher law extends from the dynamics of globular clusters up to the dynamics of groups of galaxies and how it can be consider as a modified version of Kepler's third law. With it, it will be shown how at second perturbation order lensing can be fully understood and that the corresponding PPN gamma parameter is required to be close to one. I will show how to construct a relativistic metric extension of gravity using this observational facts and briefly mention its potential for understanding the dynamics of clusters of galaxies and of the expanding universe without the need to introduce any dark matter/energy entities for its description.

Speaker: Dr Sergio Mendoza (Instituto de Astronomia, Universidad Nacional Autonoma de Mexico (UNAM))

mendoza-texas2015.pdf

18:16 Varying constants entropic cosmology

We formulate the basic framework of thermodynamical entropic force cosmology which allows variation of the gravitational constant G and the speed of light c. Three different approaches to the formulation of the field equations are presented. Some cosmological solutions for each framework are given and one of them is tested against combined observational data (supernovae, BAO, and CMB). From the fit of the data it is found that the Hawking temperature numerical coefficient γ is two to four orders of magnitude less than usually assumed on the geometrical ground value of O(1) and that it is also compatible with zero. Besides, in the entropic scenario we observationally test that the fit of the data is allowed for the speed of light c growing and the gravitational constant G diminishing during the evolution of the universe. We also obtain a bound on the variation of c to be ∆c/c ∝ 10^−5 > 0 which is at least one order of magnitude weaker than the quasar spectra observational bound.

Speaker: Hussain Gohar (University of Szczecin, Poland)

poster_v2.pdf

18:19 Kaluza-Klein cosmological model in $f(R,T)$ gravity with $\Lambda(T)

A class of Kaluza-Klein cosmological models in $f(R,T)$ theory of gravity have been investigated. In the work, we have considered the functional $f(R,T)$ to be in the form $f(R,T)=f(R)+f(T)$ with $f(R)=\lambda R$ and $f(T)=\lambda T$. Such a choice of the functional $f(R,T)$ leads to an evolving effective cosmological constant $\Lambda$ which depends on the stress energy tensor. The source of the matter field is taken to be a perfect cosmic fluid. The exact solutions of the field equations are obtained by considering a constant deceleration parameter which leads to two different aspects of the volumetric expansion namely a power law and an exponential volumetric expansion. Keeping an eye on the accelerating nature of the universe in the present epoch, the dynamics and physical behaviour of the models have been discussed. From statefinder diagnostic pair we have found that the model with exponential volumetric expansion behaves more like a Lambda cold dark matter ($\Lambda$CDM) model.

Speaker: Prof. Pradyumn Kumar Sahoo (Birla Institute of Technology and Science-Pilani, Hyderabad Campus)

18:22 A Palatini formalism for MOND in $f(\chi)$ gravity

In this work we construct a relativistic extension of the MODified Newtonian Dynamics (MOND) in the metric formalism $f(\chi)$ using the Palatini approach. We show that a simple power law: $f(\chi)=\chi^b$, with $b = 3/2$ corresponds to the non-relativistic form of MOND. Amongst the many approaches proposed to extend MOND to a relativistic regime, the Palatini metric formalism discussed here, yields second order field equations, which is a desirable (but not a necessary) requirement in a gravitational theory. We briefly discuss lensing applications of this proposal.

Speaker: Ernesto Barrientos Rodríguez (Universidad Nacional Autónoma de México)

poster.pdf

18:25 Anisotropic Spherically Symmetric Collapsing Star From Higher Order Derivative Gravity Theory

Combinations of Lovelock polynomials $R^2,R_{\mu\nu}R^{\mu\nu}$ and $R_{\mu\nu\eta\delta}R^{\mu\nu\eta\delta}$ is added with Einstein-Hilbert action to obtain interior metric of an anisotropic spherically symmetric collapsing (ASSC) stellar cloud. We assume that time dependent interior metric of the ASSC cloud is flat Minkowski at beginning of the collapse. We solved linearized metric equation and obtained convergent series solutions for the interior metric components, mass density, radial, transverse and isotropic pressures, time dependent barotropic index and dimensionless anisotropic parameter. Ricci and Kretschmann scalars for our solutions are not singular at the beginning and duration of the collapse. Mathematical calculations predict that the collapsing cloud reach to its final state (compact object) and the collapse will be stopped at a finite time $t_C$. Also we obtain particular times $t_E$ and $t_A$ where the singularity and apparent horizon are formed. Singularity can not be observed by an external observer because of $t_E>t_A>t_C$.

Speaker: Dr Hossein Ghaffarnejad (Semnan University of IRAN)

Ghaffarnejad_Contribution.pdf

Poster_Texas_2015.pdf

Proc.pdf

18:28 gap

19:30 → 21:30 Public talk

19:30 Einstein’s legacy: 100 years of general relativity

Einstein’s theory of general relativity revolutionised our understanding of the cosmos, its origin and its fate. Not surprisingly, it is one of the best tested theories, and so far all of its predictions have been confirmed. Einstein himself did not know many of the tests we can do today, 100 years after general relativity was presented by him. The most modern tests involve ultra-compact neutron stars, black holes, or ripples in space-time called gravitational waves. Perhaps surprisingly, general relativity, and the research into it, can also be encountered in daily life - perhaps well hidden, but present nevertheless. This talk will present some of the most exciting tests of general relativity, the fascinating objects that we use to study it, and reveal some of the connections to daily life.

Speaker: Prof. Michael KRAMER (Max-Planck-Institut fuer Radioastronomie)

Video (english)

Video (francais)

Wednesday 16 December

08:30 → 09:00 Registration

09:00 → 10:45 Plenary talks

09:00 Making waves: modeling gravitational waves from coalescing binary systems

Gravitational waves were first predicted by Albert Einstein in 1916 on the basis of his theory of general relativity. In the next five years ground-based interferometers, such as advanced LIGO, advanced Virgo and KAGRA, are likely to provide the first direct detections of gravitational waves from binary systems composed of black holes and/or neutron stars. In this talk, we review the progress done over the last several years at developing accurate signal models for the searches, so that we can take full advantage of the discovery potential of the detectors. We also discuss the unique astrophysical and fundamental physics information that we will be able to extract upon detection.

Speaker: Prof. Alessandra Buonanno (Max Planck Institute for Gravitational Physics)

09:35 Rattle and shine by compact binaries mergers

Compact binary systems are copious producers of gravitational waves and are also expected to radiate strongly electromagnetically. This talk will describe several processes --intrinsically requiring the strongly gravitating/highly dynamical behaviour of the system-- that can yield observable signals in a variety of frequencies. Moreover, we will discuss how such radiation might prove fundamental in answering key questions about their components and gravity itself.

Speaker: Prof. Luis Lehner (Perimeter Institute)

texas2015_lehner.pdf

Video

10:10 Experimental tests of general relativity in binary systems

The radio sky is a fascinating laboratory for a very wide range of physics. The laws of nature can be probed at a fundamental level, in particular when observing the most extreme matter in the observable universe - neutron stars. When they are visible as radio pulsars they can act as cosmic clocks that become especially interesting if they have a binary companion. Indeed, binary pulsars provide indispensable laboratories for precision tests of gravity. Effects that can be studied in great detail include the emission of gravitational waves, Shapiro delay, orbital precession and more. But also fundamental differences between general relativity and alternative theories of gravity can be probed, such as possible violations of the strong equivalence principle, preferred frame effects or the existence of gravitational dipole radiation or scalar fields. Also the effects of spin precession in strongly self-gravitating bodies can be studied by observing effects of geodetic precession. These and an other tests, and the comparison with other methods, will be discussed.

Speaker: Prof. Michael KRAMER (Max-Planck-Institut fuer Radioastronomie)

kramer_texas15.pdf

Video

10:45 → 11:20 Coffee break and poster session

11:20 → 12:30 Plenary talks

11:20 Quantum effects on black holes: evaporation, tunnelling, information leak. Anything observable?

Black holes are well understood in their classical dynamics or as background geometry for quantum fields. But their quantum gravitational properties remain elusive. These are crucial to understand what happens to the matter falling inside, and to know the holes' long term stability. There are a number of recent results and ideas on this issue, including the firewall theorem, Planck stars, graviton condensate approximations and others. There have also been suggestions for possible observable windows, for instance effects of metric fluctuations outside the horizon, or cosmic rays from by primordial black holes' decay.

Speaker: Prof. Carlo Rovelli (Université de la Méditerranée, Marseille)

plenary_1120_Rovelli.key

plenary_1120_Rovelli.pdf

Video

11:55 The LHC and the Universe

From the discovery of the Higgs boson to constraints on dark-matter interactions and on new-physics effects, the LHC run at 8 TeV has contributed greatly to our knowledge of the particle physics world. I will highlight how this knowledge is influencing advancements in the physics of the early universe and how the interplay between particle physics and cosmology will progress with the 13 TeV LHC run.

Speaker: Gian Giudice (CERN)

plenary_1155_giudice_the_LHC_and_the_universe.pdf

Video

12:30 → 14:00 Lunch break

14:00 → 15:45 05 - Dark matter

Convener: Marco Cirelli (CEA/Saclay)

14:00 Analysis update to the 2013 data from the Large Underground Xenon project

The Large Underground Xenon (LUX) project is a direct dark matter detection experiment using a dual-phase Xenon time projection chamber. The analysis has been improved for the first 90 live days of 2013 data while LUX collects another 300 live days of exposure. The enhancements include photon counting of S1, total charge measurements of S2, more calibration data, new background and signal models, and better position reconstruction. These upgrades allow for a lower energy threshold and better discrimination between signal and background events. The improved analysis still gives a null result for both Spin Independent and Spin Dependent WIMPs, therefore limits on the interaction cross sections were set. The resulting sensitivity to low mass WIMPs improved by more than a factor x100 compared with the original analysis, and the sensitivity to high mass WIMPs increased by about x1.5.

Speaker: Wing To (SLAC)

WingTo_TexasTalk.pdf

14:25 Results on light dark matter particles with a low threshold CRESST-II detector

CRESST-II is a direct dark matter search using cryogenic detectors based on calcium tungstate. Due to their light nuclei and low energy thresholds these detectors allow for a high sensitivity for dark-matter particles with low masses. We present data corresponding to an exposure of 52 kg-days obtained by one single detector module with a very low energy threshold of 307 eV for nuclear recoils. A blind analysis was performed on the data set resulting in a significantly improved sensitivity for dark-matter particles with masses below 3 GeV/c$^2$. Furthermore, this result extends the parameter space covered by direct dark matter searches to the sub-GeV/c$^2$ mass region.

Speaker: Achim Gütlein (Austrian Academy of Sciences)

presentation_LowMassLimit_CresstII.pdf

proc_LowMassLimit_CresstII.pdf

14:45 Update on Dark Matter constraints from CMB anisotropies

Cosmology, and especially the CMB anisotropies, has been proved to be a powerful tool in the quest for pinning down the nature of Dark Matter (DM). In this talk, I will review how it is possible to get very competitive constraints on the lifetime and the fraction of unstable DM particles, as well as constraints on the annihilation cross section, using either purely gravitationnial arguments, and/or from the impact of decay products on the anistropies of the CMB. I will present new results using the very last Planck data and comment on perspective on new probes for testing DM properties with Cosmology.

Speaker: Vivian Poulin (Unite Reseaux du CNRS (FR))

CMBconstraints_Symposium_VivianPoulin.pdf

proceeding_DM_halos_vivian_poulin.pdf

15:05 The formation of primordial black hole dark matter

There are strong theoretical arguments which suggest that primordial black holes (PBHs) may have formed from the collapse of large over-densities during the radiation dominated epoch shortly after the end of inflation. Because these black holes can form on much smaller scales than those visible from the CMB or large-scale structure, they have historically been used to place a unique constraint on the amplitude of the small-scale primordial power spectrum. In addition to their use in constraining the early universe, PBHs also represent a viable dark matter candidate, and the conditions required for the formation of a large enough number of PBHs to constitute dark matter will be discussed. A particular focus will be on a new method using CDM isocurvature perturbations arising from non-Gaussianity in the primordial universe. Isocurvature perturbations produced in such a manner lead to extremely tight constraints on non-Gaussianity, and provides a powerful tool to distinguish between inflationary models which could lead to the formation of PBH dark matter.

Speaker: Sam Young (University of Sussex)

05_1505_Young_The_formation_of_primordial_black_holes.pdf

05_1505_Young_The_formation_of_primordial_black_holes.pptx

15:25 Simulations of ultralight axion dark matter halos

Light scalar fields such as ultra-light axions (ULAs) are dark matter candidates which suppress the growth of perturbations on scales below their de Broglie wavelength and predict solitonic halo cores owing to their quantum pressure support. They therefore give rise to new phenomenology in large-scale structure formation and galaxy evolution, including a potential solution to the cusp-core and satellite problems. The nonlinear, non-relativistic dynamics of ULA halos can be described by the Schroedinger-Poisson equations or, equivalently, the fluid equations with an additional pressure term. Several approaches to simulate structure formation with ULA dark matter and some preliminary results will be presented.

Speaker: Jens Niemeyer (Goettingen University)

05_1525_Niemeyer_Simulations_of_ultralight_axions.key

05_1525_Niemeyer_Simulations_of_ultralight_axions.pdf

14:00 → 15:45 14 - Disks and jets

Convener: Thierry Courvoisier (University of Geneva)

14:00 Highlights on massive winds from AGN

I will briefly review the evidence for high-velocity (mildly relativistic) and massive winds in Active Galactic Nuclei. I will then highlight some new recent results obtained in X-rays (mostly using deep XMM and Chandra observations) and at multi-frequencies for both low-z AGNs and high-z QSOs. Among other things, these studies indicate that massive, high-velocity, outflows may be more common than previously thought.

Speaker: Massimo Cappi (National Institute for Astrophysics - INAF)

14_1400_Cappi_highlights_on_massive_winds_review.pdf

14_1400_Cappi_highlights_on_massive_winds_review.pptx

14:22 High Energy flares of FSRQs

High-Energy gamma-ray flares (E$>$10 GeV) of Flat Spectrum Radio Quasars (FSRQ) give us strong constraints of jet-physics, and of the surrounding-medium. We performed the first study of these flares, examining FERMI-LAT archival-data, and triggering $\sim$40 ToO-observations from near-ir to TeV (e.g., for PKS 1441+25), at the occurrence of new flares. We identified $\sim$260 gamma-ray flares. Among these, we investigated peculiar and short-flares of 3C454.3 and CTA102, showing remarkably hard gamma-ray spectra. We show here the study of a sample of 12 FSRQs, and we discuss the broad-band spectra, and variability-timescales in terms of injection and cooling of energetic-particles, arguing that these flares originate at parsec distance from the Supermassive Black-Hole, powered by magnetic-reconnections or turbulence in the flow. For the whole sample of 260 flares, we will show spectral and temporal properties, and the correlation with disk luminosity during flares. *emphasized text*

Speaker: Luigi Pacciani (IAPS/INAF)

14_1421_PACCIANI_High_Energy_Flares.pdf

14:42 Relativistic Speeds and Transverse Velocity Structure on 50 kpc Scales in NGC6251

We present new, deep, high-resolution images of the iconic jets in the nearby radio galaxy NGC 6251 made with the Karl G. Jansky VLA, resolving the faint counter-jet in width for the first time. We model the jet velocity field using the method of Laing & Bridle (2002, 2014). We assume that the jets are intrinsically symmetrical, axisymmetric, stationary flows and fit to images of linear polarization as well as total intensity. We show that the jets have transverse velocity structure, with a high Lorentz factor spine surrounded by a mildly relativistic shear layer. The jets in NGC6251, unlike those we have studied previously, maintain high speeds out to at least 50 kpc from the nucleus rather than decelerating rapidly. The dominant magnetic field component in the jet is longitudinal close to the nucleus and toroidal at large distances.

Speaker: Robert Laing (ESO)

14_1442_Laing_Relativistic_speeds.pdf

15:02 The accretion-ejection connection in the Galactic black hole candidate X-ray binary MAXI J1836-194

There is a universal connection between the accretion and ejection phenomena that are observed in black holes across the mass scale. Quantifying this relationship is the first step in understanding how jets are launched, accelerated and collimated. X-ray binaries are ideal systems to study this relationship, as they evolve on human timescales. In outburst, their luminosities increase by several orders of magnitude, with the X-ray emission from the accretion disk and the radio emission from the relativistic jets undergoing dramatic, coupled changes. I will present the results of a multiwavelength radio through to X-ray observing campaign of the Galactic black hole candidate X-ray binary MAXI J1836-194 during its 2011 outburst. Our simultaneous observations provide an unprecedented insight into the processes occurring around a black hole during outburst, allowing us to track the evolution of the launching region of the jet as the accretion flow changes. This will help to understand the launching of accretion-powered jets on all scales, from X-ray binaries to their larger-scale analogues, AGN.

Speaker: Dr Thomas Russell (ICRAR/Curtin University)

Texas2015_TRussell.pdf

15:22 GRS 1915+105 and its spectral variability from the keV to the MeV band

The microquasar GRS 1915+105 features well known spectral states that were never extensively studied up to the MeV range, where key spectral diagnostics are expected. We present hard X-ray observations obtained in 15 Msec with Swift/BAT and INTEGRAL and spectra collected during different states up to 400 keV. These spectra can be successfully fitted by the EQPAIR model revealing continuous variations of the model parameters, including the inner radius of the accretion disc, along the sequence of spectral states.

Speaker: Dr Marek Nikolajuk (University of Bialystok)

14_1522_Nikolajuk_GRS_1915105_and_its_spectral_variability_from_the_keV_to_the_MeV_band.pdf

15:42 Coeval observations of a complete sample of flat-spectrum blazars with Effelsberg, IRAM 30m, and Planck

We present time-resolved broad-band spectra of a complete sample of blazars, selected by showing flat radio spectra up to 143 GHz, taken from observations with Planck, the Effelsberg 100m telescope, and the IRAM 30m telescope. Dedicated Effelsberg observations have been focused on times within two months around Planck single survey scans of each source, with a cadence of 2-4 weeks during the 4th and 5th Planck survey. The data are complemented with flux measurements from the F-GAMMA program (Fuhrmann et. al, 2007, AIPC 921, 249; Fuhrmann et al., 2014, MNRAS 441, 1899), and from other Effelsberg and IRAM monitoring programs, as far as available. Planck data are extracted employing methods used in the blind search for variable sky signals, which allow to estimate snap-shot source fluxes down to pointing period (i.e. hour scale) time resolution (Rachen et al., Proc IAU GA 2015). The program thus covers 15 frequencies between 2.4 to 857 GHz and is sensitive to variability time scales from hours over weeks up to one year, which is unprecedented in the history of blazar monitoring.

Speaker: Jörg Paul Rachen (IMAPP / Radboud University Nijmegen)

JPR_PlanckEff.pdf

JPR_PlanckEff_proc.pdf

JPR_PlanckEff_talk.pdf

14:00 → 15:45 15 - Binaries: Millisecond pulsars

Convener: Alessandro Papitto

14:00 Millisecond pulsars: on their own, with a friend, or even two

As the most rapidly rotating stars known, millisecond pulsars continue to enjoy great scientific interest and broad impact. They acquire their millisecond rotational periods through mass transfer from a binary stellar companion; via their radio, X-ray and/or gamma-ray pulsations we can precisely time their spin rate and orbital motion around a companion object (or even multiple companions). Millisecond pulsars are thus not only exotic stars in their own right, but also precision astronomical clocks for measuring other physical effects in extreme environments. In this review talk, I will discuss how the large recent increase in known millisecond pulsars is shaping our understanding of their formation/evolution and is enabling ever more constraining tests of gravitational theories and dense matter physics.

Speaker: Dr Jason Hessels (University of Amsterdam)

15_1400_Hessels_Millisecond_pulsar.pdf

14:30 THE YOUNG, RELATIVISTIC BINARY PULSAR J1906+0746

PSR J1906+0746 is a young pulsar in the relativistic binary with the second-shortest known orbit, of 3.98 hours. We will present a timing study based on five years of observations, conducted with the 5 largest radio telescopes in the world, aimed at determining the companion nature (van Leeuwen et al. 2015). Through the measurement of three post-Keplerian orbital parameters we find the pulsar and companion masses to be 1.323(11)M⊙ and 1.290(11)M⊙ respectively. These masses are compatible with a neutron star companion, but also fit well in the known mass distribution of white dwarfs around young pulsars such as J1906+0746. Neither radio pulsations nor any dispersion-inducing outflows that could have established the companion nature were detected. We derive an HI-absorption distance, which indicates an optical confirmation of a white dwarf companion is very challenging. The pulsar is fading fast due to geodetic precession, limiting future timing improvements. We conclude that young pulsar J1906+0746 is either part of a binary neutron star, or is orbited by an older white dwarf, in an exotic system formed through two stages of mass transfer.

Speaker: Joeri van Leeuwen (ASTRON / U. Amsterdam)

15_1430_Van_Leeuwen_Session15_J1906+0746_v02.pdf

15_1430_Van_Leeuwen_Session15_J1906+0746_v02.pptx

14:55 Two new relativistic MSPs from the HTRU-North

We report on the two new MSP discoveries from the High Time Resolution Universe survey for pulsars and fast transients in the northern hemisphere (HTRU-North), being conducted with the 100-m Effelsberg telescope (Barr et al, 2013). The survey has so far resulted in the total number of 17 new pulsars. Here we present timing solutions for PSR J2045+3633 and PSR J2053+4650, both binary systems with massive companions (>0.8 M☉). Our objective is a precise mass measurement of the components of these binary systems. PSR J2045+3633 has a spin period of 31.68 ms, orbital period of 32.3 days and orbital eccentricity e = 0.017. Such eccentricity, high for pulsar-white dwarf systems and low for double neutron star systems, indicates that this pulsar probably accreted very little matter from the massive, short-lived progenitor of its companion whose nature is not totally clear yet. Systems with eccentricities in this range are rare so are important for understanding the mildly-recycled pulsar population. Measuring their masses, we improve the sample of NS masses “at birth". After one year of timing with the Effelsberg, Jodrell Bank, Arecibo and Nançay telescopes the derived pulsar mass estimate is 1.64±0.27 M☉. The precision continues to improve quickly. PSR J2053+4650 has a spin period of 12.58 ms and a highly-inclined (84.5°) circular 2.45-day orbit with a white dwarf companion. This high orbital inclination contributed to the detection of the Shapiro delay in the first timing campaign with the Effelsberg telescope, which, in turn, combined with the Jodrell Bank and Nançay observations, allowed us to measure the pulsar mass up to 16% precision: 1.52±0.25 M☉ . Both pulsars are very bright (timing residuals of order 2 μs for 30-minute observations are obtained with Effelsberg) and promise to be a valuable addition to the pulsar timing arrays.

Speaker: Marina Berezina (Max Planck Institute for Radio Astronomy)

15_1455_BEREZINA_two_new_relativistiv_MSPs.pdf

15:15 Simultaneous X-ray and Radio observations of mode-switching radio pulsars PSR B0943+10 and PSR B1822-09

With XMM-Newton, GMRT and LOFAR observations of the mode-changing near-aligned pulsar PSR B0943+10 we discovered synchronous switching in the radio and X-ray emission properties (Hermsen et al. 2013). These extraordinary findings were reported to support radio indications for rapid, global changes to the conditions in the magnetosphere. However, there is still no consistent interpretation for the X-ray mode switching. PSR B1822-09 is a fascinating pulsar exhibiting similar mode switching in the radio band. Mode switching in the radio emission of PSR B1822-09 is not only seen in its main-pulse and precursor emissions (like for PSR B0943+10), but also in that of its inter pulse. The latter switches in anti correlation with the main pulse. Radio data on PSR B1822-09 strongly suggest that it is an orthogonal rotator, but a near-aligned geometry is also discussed in literature. We organised for this pulsar in 2013-2014 a similar campaign of simultaneous XMM-Newton, GMRT, WSRT and Lovell observations. PSR B1822-09 does not show X-ray mode switching and exhibits X-ray characteristics that differ from those reported for PSR B0943+10, and that do not support the geometries discussed based on its radio properties. In this presentation we will compare the results from the two X-ray radio campaigns and discuss these in the context of competing theoretical emission models. Hermsen et al., 2013, Science 339, 436

Speaker: Prof. Wim Hermsen (SRON Netherlands Institute for Space Research, Utrecht, The Netherlands)

Hermsen PSR1822-09 Texas Symposium.pdf

14:00 → 15:45 16 - Black holes

Convener: Didier Barret (IRAP (UPS/CNRS))

14:00 General relativistic precession of orbits around the stellar-mass black hole in H 1743-322

Accreting stellar mass black holes often show a quasi-periodic oscillation (QPO) in their X-ray flux with a period that slowly drifts from ~10s to ~0.05s and an iron emission line in their X-ray spectrum. The iron line is generated by fluorescent re-emission, by the accretion disk, of X-ray photons originating in the innermost hot flow. The line shape is distorted by relativistic motion of the orbiting plasma and the gravitational pull of the black hole. The QPO arises from the immediate vicinity of the black hole, but so far its physical origin has remained unknown. I will present observations of the iron line in the black hole binary H 1743-322 where we find that the line energy varies quasi-periodically, in step with the ~4.5s QPO cycle. This result provides strong evidence that this class of QPO originates via Lense-Thirring precession, a General Relativistic effect causing the inner flow to precess as the spinning black hole twists up the surrounding space-time. This is the first demonstration of Lense-Thirring precession in the strong field regime of General Relativity. The precession occurs at a rate 14 orders of magnitude faster than in all previously reported examples, in the Earth’s gravitational field. Our result enables the application of tomographic techniques to precisely map the motion of matter in the strong gravity near black hole event horizons.

Speaker: Dr Adam Ingram (University of Amsterdam)

14:25 On the Detection of an Extreme Gravitationally Redshifted Fe-line constraining the Rotation of the Super-Massive Black Hole in Mrk 876

Most galaxies undergo one or more eras of Active Galactic Nucleus (AGN) activity throughout their existence. During this era their environment around the central super-massive black hole emits from X-ray to soft gamma-ray energies. Therefore these spectra and their features carry the information of the extreme gravitational conditions. However these spectral features can be transient and shifted to unexpected energies making their detection difficult. We present our recent results of a case study on the AGN Mrk 876. The detection of a transient and extreme gravitationally redshifted Fe-line allows us to find its emission mechanism, thereby constraining the rotation of the super-massive black hole in the center of Mrk 876. This finding together with a morphological study of the source allows for conclusions on the mechanism that switched on the AGN activity in Mrk 876.

Speaker: Eugenio Bottacini (Stanford University)

14:47 The high energy variability of V404 Cygni during the June 2015 outburst

The black hole binary V404 Cygni exhibited an unprecedently bright outburst on 2015, June 15. Since then, many space and ground observing facilities monitored the flux from the source during several weeks, until its decline to a near-quiescent state in late July-August. The source was extremely variable at all wavelenghts. The radio versus X-ray flux variations are reminiscent of the already observed correlation in this and other black hole sources, in which the luminosity is dominated by jet emission. The high energy instruments on board INTEGRAL detected an extremely variable emission during both bright and low luminosity phases, with dramatic variations of the hardness ratio on time scales of ~seconds. The analysis of the IBIS and SPI data reveals the presence of hard spectra in the brightest phases, compatible with thermal Comptonization with plasma temperature ~40 keV. On the other hand, the soft (<10 keV) X-ray spectra observed by Swift, Chandra and NuSTAR show large absorption column variations and indication for strong disk outflows. Given the strong hardness variations detected in the range ~20-200 keV, we conclude that the overall variability originates from two distinct components, the first due to absorption and the other originating very close to the central accreting source, most probably related to relativistic ejection events.

Speaker: Lorenzo Natalucci (Istituto di Astrofisica e Planetologia Spaziali, INAF)

V404_Texas_Natalucci_web.compressed.pdf

15:12 Measuring the Innermost Stable Circular Orbits of Supermassive Black Holes

We present a promising new technique (g-distribution method) for measuring the innermost stable circular orbit (ISCO), the inclination angle (i), and the spin of a supermassive black hole. The g-distribution method involves measurements of the distribution of the energy shifts of the relativistic iron line emitted from the accretion disk of a supermassive black hole that is microlensed by stars in a foreground galaxy and a comparison of the measured g-distribution with microlensing caustic simulations. The method has been applied to the gravitationally lensed quasar RX J1131−1231 and initial results indicate that r_ISCO < 9 gravitational radii and i < 60 degrees. Further monitoring of RX J1131−1231 and other lensed quasars will provide tighter constraints on the inclination angles, ISCO radii and spins of the black holes of distant quasars.

Speaker: Dr George Chartas (College of Charleston)

texas15_chartasg.pdf

texas15_chartasg.pptx

15:33 MHD Shocks in Accretion onto a Rotating Black Hole

The formation of standing magnetohydrodynamical (MHD) shocks by accreting plasma in a black hole magnetosphere is studied. The black hole magnetosphere would be formed around a black hole with an accretion disk. The global magnetic field lines would be originated by currents in the accretion disk and its corona, and then some part of magnetic field lines would lead to the event horizon. Along such magnetic field lines magnetized plasma streams from the disk surface to the horizon, and on the way to the horizon MHD shock can be generated. Although the postshock plasma becomes very hot, the MHD shock can be expected as a source of high-energy radiation, which is generated very close to the horizon and then carry to us a lot of information of the black hole spacetime. We also discuss the huge energy release at the MHD shock front, where the plasma's kinetic energy and the black hole's rotational energy can convert to radiative energy by considering negative energy postshock MHD flows (Takahahi & Takahashi 2010). This means that the Blandford-Znajek (1977) power can convert to radiative energy at the MHD shock generated very close to the horizon.

Speaker: Masaaki Takahashi (AIchi University of Education)

Texas2015_Takahashi.pdf

Texas2015_Takahashi_talk.pdf

15:36 Accretion of a relativistic kinetic gas into a black hole

We analyze the accretion of gas into a black hole background space-time in the context of relativistic kinetic theory. The state of the gas is described by a distribution function which has to satisfy the general relativistic Boltzmann equation. In the first part of this work, we describe a method to find the most general solution of this equation in the collisionless case. In the second part, we apply our result to the case of a radial flow propagating on a nonrotating black hole. We compute the accretion rate and compare it to the one of the Michel fluid flow solution, clarifying previous results in the literature.

Speaker: Ms Paola Rioseco (IFM-UMICH)

posterpres-PRioseco.pdf

proc-poster-accretion.pdf

15:39 Angular momentum loss by gravitational radiation in binaries with black hole

In this study, we present angular momentum loss mechanism through gravitational radiation for the selected X-ray binary systems. Gravitational radiation time-scale is estimated for each selected system. In addition, their gravitational wave amplitudes are also estimated and their detectability with gravitational wave detectors has been discussed.

Speakers: Ms Dolunay Kocak (University of Ege), Kadri Yakut (University of EGE)

proc_DKocak.pdf

15:42 Quasi-periodic oscillations of perturbed tori

Our research focuses on axisymmetric hydrodynamical simulations. The models implemented are *thinner* tori and *thicker* torus in equilibrium around a non-rotating black hole. The tori were constructed with a constant distribution of angular momentum obtained from Kluzniak-Lee (a pseudo-Newtonian) potential. Epicyclic motion were triggered by adding sub-sonic velocity fields; radial, vertical and diagonal. As the perturbed tori evolved in time, we measured $L_{2}$ norm of density and obtained the power spectrum which manifested modes as predicted by theory. Results from our simulations are relevant in the context of high-frequency quasi-periodic oscillations (HF QPOs) observed in stellar-mass black hole binaries.

Speaker: Mr Varadarajan Parthasarathy (N. Copernicus Astronomical Center)

QPO_Texas15.pdf

14:00 → 15:45 11 - Gravitational waves

Convener: Chiara Caprini (CEA-Saclay)

14:00 The quest for a stochastic background with LIGO/VIrgo GW detectors

According to various cosmological scenarios, we are bathed in a stochastic background of gravitational waves generated in the first instants after the Big Bang. Detection of this background would have a profound impact on our understanding of the evolution of the Universe, as it represents a unique window on the very early Universe and on the physical laws that apply at the highest energy scales. In addition to the cosmological background, an astrophysical background may have resulted from the superposition of a large number of unresolved sources since the beginning of stellar activity. This astrophysical contribution could be a foreground masking the cosmological background but it can also provide very interesting informations, not only about the physical properties of the respective astrophysical populations, complementing individual GW detections, but also about the evolution of these objects with redshift, the star formation history or the metallicity. In this talk, I will give an overview of the different sources and present the data analysis methods used in the LIGO/Virgo collaboration to measure the energy density of the GW background. I will discuss the first 3-months observational run of Advanced LIGO (fall 2015) as well as the accessibility of the different models and the constrains we expect to put on their parameters in the next few years and with third generation detectors like Einstein Telescope.

Speaker: Tania Regimbau (Observatoire de la Côte d'Azur)

11_1400_Regimbau_the_quest_for_a_stochastic_background.pdf

11_1400_Regimbau_the_quest_for_a_stochastic_background.pptx

14:21 Cosmic variance in the nanohertz gravitational wave background

We use large N-body simulations and empirical scaling relations between dark matter halos, galaxies, and supermassive black holes to estimate the formation rates of supermassive black hole binaries and the resulting low-frequency stochastic gravitational wave background (GWB). We find that uncertainty in the astrophysical scaling relations systematically changes the amplitude of the GWB by a factor of ∼2, and that this range is already constrained by recent pulsar timing array upper limits. We investigate the Poisson variance in the amplitude of the GWB for randomly-generated populations of supermassive black holes, finding a scatter of order unity per frequency bin below 10 nHz, and increasing to a factor of ∼10 near 100 nHz. This variance is a result of the rarity of the most massive binaries, which dominate the signal, and acts as a fundamental uncertainty on the amplitude of the underlying power law spectrum. This Poisson uncertainty dominates above 20 nHz, while at lower frequencies it is subdominant to that due to our poor understanding of the astrophysical scaling relations. At very low frequencies, uncertainties related to the final parsec problem and the processes which drive binaries to the gravitational wave dominated regime may affect both the astrophysical and Poisson variance in the spectrum of the GWB.

Speaker: Elinore Roebber (McGill University)

Roebber_cosmic_variance_nHz_gwb.pdf

14:42 Gravitational Waves from a Dark Sector

A large class of models with a composite dark sector undergo a strong first order phase transition in the early universe, which could lead to a detectable gravitational wave signal. I will summarise the basic conditions for a strong first order phase transition for SU(N) dark sectors, calculate the gravitational wave spectrum and show that, depending on the dark confinement scale, it can be detected at eLISA or in pulsar timing array experiments. The gravitational wave signal provides a unique test of the gravitational interactions of a dark sector, and we discuss the complementarity with conventional searches for new dark sectors.

Speaker: Pedro Klaus Schwaller

GW_Texas_2015.pdf

15:03 Acoustically generated gravitational waves from thermal first order phase transitions

Recent numerical simulations have demonstrated that the most important source of gravitational radiation from a thermal first order phase transition in the early Universe is the sound waves it produces. I outline the theory of the acoustic production of gravitational waves from phase transitions, showing how both the amplitude and shape of the power spectrum can be simply understood. Implications for the detectability of a first-order electroweak transition by future space-based detectors will be briefly discussed.

Speaker: Mark Hindmarsh (University of Sussex)

G-Waves 2015 Texas Hindmarsh.pdf

G-Waves 2015 Texas Hindmarsh.pptx

15:24 Gravitational waves from a thermal first order phase transition: numerical simulations

We present large-scale numerical simulations of the gravitational radiation produced by a first order thermal phase transition in the early universe. The dominant source of gravitational waves is sound waves generated by the expanding bubbles of the low-temperature phase. The resulting gravitational wave power spectrum has a power-law form between scales set by the average bubble separation and the bubble wall width. However, the general form of the power spectrum is different from that predicted by the widely-applied envelope approximation, and the predicted gravitational wave energy density is at least two orders of magnitude larger.

Speaker: David Weir (University of Stavanger)

texas-weir.pdf

14:00 → 15:45 10 - Cosmic magnetic fields: Origin, evolution and signatures

Convener: Tina Kahniashvili

14:00 Relaxing the limits on inflationary magnetogenesis

Inflation has long been thought as the best way of producing large-scale primordial magnetic fields. To achieve fields strong enough to seed the galactic dynamo, most of the generation mechanisms operate outside conventional electromagnetic theory, which is typically restored after the end of the de Sitter phase. Breaking away from standard electromagnetism can lead to substantially stronger magnetic fields at the end of inflation and thus compensate for their subsequent adiabatic depletion. We argue that the drastic magnetic enhancements during the de Sitter era may not be necessary. In particular, we use causality arguments to claim that, contrary to the common belief, superhorizon-sized magnetic fields are not necessarily frozen into the matter after inflation. On these super-Hubble scales the magnetic decay can slow down considerably, and thus make it much easier to produce primordial fields of astrophysical interest today.

Speaker: Christos Tsagas (Aristotle University of Thessaloniki)

10_1400_Tsagas_Relaxing_the_limits.pdf

proceedings.pdf

14:21 Relativistic chiral magnetohydrodynamics and evolution of cosmological magnetic fields

If chiral (left-right) asymmetry is present in the plasma, the electric current, parallel to the magnetic field, appears. This is known as "*chiral magnetic effect*". We demonstrate that this effect changes the dynamics of the magnetized relativistic plasma and present the proper equations of chiral relativistic magnetohydrodynamics, containing a new, axion-like, degree of freedom. There results are relevant for generation and evolution of cosmological magnetic fields in the electroweak epoch and are applicable to other relativistic plasmas.

Speakers: Dr Alexey Boyarsky (Leiden University (NL)), Oleg Ruchayskiy (Ecole Polytechnique Federale de Lausanne (CH))

Ruchayskiy_Texas.pdf

14:42 First numerical simulations of the chiral MHD dynamo effect

Under extreme conditions, e.g. at high temperatures like in the early Universe, the usual magnetohydrodynamical (MHD) equations need to be extended. The origin of the modification is the asymmetry of the chemical potential of right- and left-handed fermions. To describe the evolution of a plasma, additional terms as well as new equations for the chiral chemical potential have to be included. We have implemented these extensions in the Pencil Code, which is a high-order finite-difference code developed for solving compressible MHD. We study laminar dynamos and find an exponential increase of the magnetic energy with the growth rate depending on the chemical potential. We further analyze the evolution of magnetic fields in the presence of turbulence. Potentially, chirality has interesting effects on the properties of magnetic fields in the early Universe and in particular on the evolution of magnetic helicity which is directly coupled to the chiral chemical potential.

Speaker: Jennifer Schober

TEXAS_2015.pdf

15:03 Evolution of primordial magnetic fields

There was a time when primordial magnetic fields posed a serious contender to explaining the origin of magnetic fields in galaxies and on larger scales. This has changed drastically during the past three decades, and now the dynamo origin of galactic magnetic fields is unchallenged. Nevertheless, primordial magnetic fields might still be an attractive possibility to explaining magnetic fields between clusters of galaxies, which are difficult to get magnetized by astrophysical mechanisms such as outflows from active galactic nuclei. Primordial magnetic fields generated during the electroweak phase transition, for example would decay during much of their subsequent evolution, but helicity slows down the decay by inverse cascading the field to larger scales. Dynamo-generated magnetic fields, on the other hand, also tend to be helical, if the dynamo operates in the presence of rotation and stratification. In my talk, I will focus on the evolution of primordial magnetic fields using numerical simulations. In the presence of magnetic helicity, inverse transfer from small to large scales is well known in magnetohydrodynamic (MHD) turbulence and has applications in astrophysics, cosmology, and fusion plasmas. Using high resolution direct numerical simulations of magnetically dominated self-similarly decaying MHD turbulence, we report a similar inverse transfer even in the absence of magnetic helicity. We compute for the first time spectral energy transfer rates to show that this inverse transfer is about half as strong as with helicity, but in both cases the magnetic gain at large scales results from velocity at similar scales interacting with smaller-scale magnetic fields. This suggests that both inverse transfers are a consequence of a universal mechanisms for magnetically dominated turbulence. Possible explanations include inverse cascading of the mean squared vector potential associated with local near two-dimensionality and the shallower k^2 subinertial range spectrum of kinetic energy forcing the magnetic field with a k^4 subinertial range to attain larger-scale coherence. The inertial range shows a clear k^-2 spectrum and is the first example of fully isotropic magnetically dominated MHD turbulence exhibiting weak turbulence scaling.

Speaker: Axel Brandenburg (Nordita)

Geneva15.pdf

15:24 MHD Turbulence and Particles

MHD Turbulence is a strongly nonlinear dynamics of conductive fluids, e.g. plasma. Recent progress in theory regarding almost all basic regimes of this dynamics -- from how the magnetic field is generated (dynamo problem), to how turbulence is decaying, to what are the asymptotic scaling laws, allowed us to proceed with more observationally motivated questions. One of them is why almost all strongly magnetized environments are indeed observable, e.g. why such environments are infused with high-energy particles, their distributions stretching to energies orders of magnitude higher than thermal. Another basic question is why plasma distribution function at low energies is also non-thermal. I will offer a couple of generic mechanisms derived based on the ideas we developed in turbulence, which may explain some of these basic facts.

Speaker: Andrey Beresnyak (Naval Research Laboratory)

texas2015.pdf

14:00 → 15:45 19 - VHE & CR: VHE observations

Convener: Teresa Montaruli

14:00 The H.E.S.S. Extragalactic Sky

The High Energy Stereoscopic System H.E.S.S. is an array of 5 Imaging Atmospheric Cherenkov Telescopes located in the Khomas Highland, Namibia. The first four 12m-diameter telescopes are operating since 2003 and a fifth telescope (a 28m diameter dish) had been added to the array in 2012 improving the sensitivity of the array towards lower energies. In this talk, I will present highlight of recent results of H.E.S.S. on AGN observations such as blazars (PKS 2155-304, Mrk 501, PG 1553+113, 1ES 0229+200) but also non-blazars AGNs (e.g radio-galaxies), extragalactic background light (EBL) and an update on the H.E.S.S. Gamma-Ray Burst program.

Speaker: Jill Chevalier (LAPP)

19_1400_Chevalier_The_hess_extragalactic_sky.pdf

proc_texassymp_chevalier.pdf

14:25 MAGIC latest results

MAGIC is a ground-based astrophysics instrument for measuring gamma rays in the energy range ~ 35 GeV - 50 TeV. It is the first instrument paving the road into the sub-100 GeV gamma-ray sky. MAGIC consists of two 17m diameter, F/1.03 imaging atmospheric Cherenkov telescopes, which are separated by 85m distance and are located at 2200m a.s.l. in the Roque de los Muchachos European North Observatory on the Canary island of La Palma. This talk will provide a review of the most important results recently obtained by the MAGIC collaboration. They include a substantial list of flaring episodes detected from AGN, leading to the discovery of VHE emission from redshift close to 1 and constraints on the EBL. In our galaxy, MAGIC measured the spectrum of gamma-rays from the Crab pulsar extending from few tens of GeV to above 1 TeV. Deep observations to search for dark matter as well as other results on fundamental physics will also be reported.

Speaker: Oscar Blanch (IFAE)

2015-12_TexasSym_magic_highlights_v2r0.pdf

14:50 Recent Science Highlights from VERITAS

VERITAS is a very-high-energy (VHE, E$&#x2273$100 GeV) gamma-ray observatory that has been in full scientific operation since 2007. A series of upgrades has provided significant sensitivity increases and improved low-energy performance, greatly enhancing the scientific capabilities of VERITAS. The VERITAS science program includes a full complement of observations of Galactic (pulsars, pulsar-wind nebulae, supernova remnants, binary systems) and extragalactic objects (blazars, radio and starburst galaxies, gamma-ray bursts), in addition to cosmic ray studies and indirect searches for dark matter. To date, VERITAS has detected more than 50 sources of VHE gamma rays from eight source classes. Highlights of the most recent VERITAS results will be presented.

Speaker: John Quinn (University College Dublin)

19_1450_Quinn_Recent_Science_highlights_from_VERITAS.pdf

15:15 Exploring the TeV Universe with HAWC

The High Altitude Water Cherenkov (HAWC) observatory is an extensive air shower detector optimized for studying gamma rays with energies between 100 GeV and 100 TeV. Located at an elevation of 4100 m near Puebla, Mexico, the array consists of 300 water tanks instrumented with 4 photo-multiplier tubes each and was completed in March 2015. A wide instantaneous field of view of ~2 sr and a duty cycle >95% allow HAWC to survey 2/3 of the sky every day. These unique capabilities make it possible to perform an unprecedented survey of TeV emission over most of the northern and part of the southern sky in order to map galactic and extra-galactic particle acceleration sites and search for gamma rays from dark matter annihilation and decay. HAWC is also ideally suited to monitor variable gamma-ray fluxes and search for flares from active galactic nuclei, gamma-ray bursts, and other transient events, providing new insights into relativistic particle acceleration in astrophysical environments. We will present results from the first years of gamma-ray and cosmic-ray observations during the evolution of HAWC from a partial array to the completed observatory. Efforts to enhance our understanding of the high energy Universe through multi-wavelength and multi-messenger analyses will also be highlighted.

Speaker: Dr Robert Lauer (University of New Mexico)

rlauer_hawc2015.pdf

14:00 → 15:45 03 - Modifications of gravity

Convener: Anne-Christine Davis (Cambridge University)

14:00 Aspects of infrared non-local modifications of General Relativity

We introduce some recently proposed non-local infrared modifications of general relativity. We discuss which are the motivations to introduce non-localities in a theory of gravity. We then present a particular class of models which has been recently shown to be cosmologically viable, with an extremely good compatibility with cosmological data. We present the general features of such a class of non-local models and we briefly review some recent developments in the understanding of the nature of non-localities.

Speaker: Ms Giulia Cusin (University of Geneva)

03_1400_Cusin_Aspects_of_infrared_non_local_modifications.pdf

14:21 Beyond General Relativity: The Geometric Deformation and New Black Hole Solutions

In the context of extra-dimensional gravity, as the Randall-Sundrum brane-world, a consistent extension of the minimal geometric deformation approach (MGD) is used to study the exterior spacetime around spherically symmetric self-gravitating system. A modified Schwarzschild geometry is obtained and new black hole solutions are shown. A possible extension of this approach in $F(R)$ theories is also presented.

Speaker: Jorge Ovalle (Simon Bolivar University)

OVALLE.pdf

14:43 Linearly shielded modifications of gravity

Modifications of gravity arising in the presence of a nonminimally coupled scalar field and capable of accelerating the expansion of our Universe can be suppressed at the linear level of cosmological perturbations, only introducing deviations from concordance cosmology at the largest observable scales. I will classify the theory space capable of this mechanism in the effective field theory of unified dark energy and discuss potentially observable signatures in relativistic effects of galaxy clustering near the Hubble scale.

Speaker: Dr Lucas Lombriser (University of Edinburgh)

Texas_2015_Lombriser.pdf

15:04 Initial conditions for simulations of arbitrary modified gravity, beyond quasi-static approximations

I will present a novel description for setting initial particle displacements and field values under arbitrary metric theories of gravity, for perfect and imperfect fluids with arbitrary characteristics. We extend the Zel'dovich Approximation to nontrivial theories of gravity, and show how scale dependence implies curved particle paths, even in the entirely linear regime of perturbations. Initial conditions set at high redshifts are affected at the level of up to 5% at Mpc scales, which exemplifies the importance of going beyond ΛCDM initial conditions for modifications of gravity outside of the quasi-static approximation. Our description paves the way for simulations and mock galaxy catalogs under theories of gravity beyond the standard model, crucial for progress towards precision tests of gravity and cosmology.

Speaker: Wessel Valkenburg (Leiden University)

wvAtTexasGeneva_MG.key

wvAtTexasGeneva_MG.pdf

15:25 gap

15:45 → 16:15 Coffee break and poster session

16:15 → 18:45 05 - Dark matter

Convener: Marco Cirelli (CEA/Saclay)

16:15 Indirect searches for dark matter in the gamma-ray sky with the Fermi LAT status and prospects

Indirect dark matter (DM) searches rely on detection of stable by-products of DM interactions to search for a signal of this elusive component of the Universe. Among these final products, gamma rays have recently played a major role in understanding the nature of the DM particle. This contribution reviews the current status of indirect DM searches with the Large Area Telescope, the main instrument on board the Fermi gamma-ray space telescope. In the absence of any conclusive DM signal, Fermi provides some of the most constraining DM limits obtained so far. Some prospects with future data and/or instruments will also be presented.

Speaker: Dr Johann Cohen-Tanugi (LUPM, Université de Montpellier & CNRS/IN2P3)

Texas_DM_JCT.pdf

16:40 Dark matter and fundamental physics with the Cherenkov Telescope Array

The Cherenkov Telescope Array (CTA) is a worldwide project aiming at building the next ground based gamma-ray observatory with a sensitivity ten times better than current experiments like H.E.S.S., MAGIC and VERITAS. CTA will be composed of several tens of telescopes with different sizes distributed on two sites located in the northern and southern hemispheres. CTA will also have a much wider energy coverage and improved angular resolution. The presentation will describe the science program on dark matter and fundamental physics.

Speaker: Emmanuel Moulin (CEA Saclay)

Moulin_DMFP_Texas2015.pdf

17:05 Dark matter ultracompact minihalos and the small-scale early Universe

In this talk I will discuss recent efforts to detect dark matter 'ultracompact minihalos' (UCMHs), including a novel utilisation of gravitational time-delay lensing with pulsars. Recently proposed as a type of small-scale dark matter structure, UCMHs are formed from large overdensities in the very early Universe. They have been shown to be able to persist through to the present day, providing a unique opportunity to investigate the conditions of the Universe at early times. I will present recent results constraining the number of UCMHs within the Milky Way, and discuss their implied limits on three processes that lead to their formation: increased primordial power on small scales, primordial non-Gaussianity, and the presence of high-tension cosmic string loops.

Speaker: Hamish Clark (University of Sydney)

05_1705_Clark_Dark_matter_ultracompact_minihalos_and_the_small-scale_early_Universe.pdf

05_1705_Clark_Dark_matter_ultracompact_minihalos_and_the_small-scale_early_Universe.pptx

17:30 Dark matter searches with antideuterons

Antideuterons can be produced through the nuclear coalescence of the antiprotons and the antineutrons that are originated in a dark matter pair annihilation or decay event. At low kinetic energies, the fluxes of these bound states are found to dominate over the astrophysical background and thus antideuterons may be considered as a very promising channel for a dark matter indirect detection, especially for WIMPs with a low or intermediate mass. In this talk, an overview on the principal issues related both to the antideuterons production and to their subsequent propagation through the interstellar medium and the heliosphere will be given. Then, the capability of current and future experiments to detect an antideuteron flux produced by dark matter annihilation will be investigated in relation to the constraints on the dark matter annihilation cross section that can be derived from the latest measurements of the cosmic antiproton flux.

Speaker: Andrea Vittino (Universita' di Torino and INFN Torino)

Vittino_Texas.pdf

17:50 Cosmic ray positrons and antiprotons: implications for Dark Matter

Using the updated proton and helium fluxes just released by the AMS-02 experiment we reevaluate the secondary astrophysical positron and antiproton fluxes. We compare our results with the positron flux and the preliminary antiproton to proton ratio, both measured by AMS-02. The main uncertainties for the theoretical calculation are assessed. For positrons, we test the possibility to explain the measured excess with a Dark Matter scenario and we probe the parameter space for the Dark Matter component. Then, we examine the possibility to explain the data with the contribution of one single pulsar. For antiprotons, we find no unambiguous evidence for a significant excess with respect to expectations. Yet, some preference for a flatter energy dependence of the diffusion coefficient starts to emerge. Also, we provide a first assessment of the room left for a Dark Matter component, deriving new stringent constraints.

Speaker: Mathieu Boudaud (LAPTh Annecy France)

boudaud_texas_2015.pdf

18:10 Astrophysical backgrounds in antiproton searches for dark matter

I review the results of a new calculation for the antiproton production by cosmic ray protons and nuclei and discuss the expected theoretical uncertainty. Then I discuss the antiproton flux expected from a local, 2 Myr old SN and the implication for indirect dark matter searches.

Speaker: Michael Kachelriess (NTNU)

05_1810__Kachelriess.pdf

18:30 The LZ Dark Matter detector

LZ is a second-generation dark-matter experiment designed to achieve unprecedented sensitivity to weakly interacting massive particles (WIMPs) of masses from a few GeV/c to hundreds of TeV/c2. With total liquid xenon mass of about 10 tonnes, LZ is planned to achieve a sensitivity to WIMP-nucleon spin-independent cross section approaching ∼2⋅10−48 cm2 in 3 years of operation. This represents an improvement of almost three orders of magnitude over current results, covering a substantial range of theoretically-motivated dark matter candidates. We will present aspects of LZ’s designs that permit achievement of this planned sensitivity.

Speaker: Bhawna Gomber (University of Wisconsin (US))

05_1830_Gomber_The_LZ_Dark_Matter_poster.pdf

LZ_Texas15_Bhawna_Talk.pdf

18:33 Axion as a cold dark matter candidate

We show that the axion as a coherently oscillating scalar field acts as a cold dark matter (CDM) to the second-order perturbations in all cosmological scales including the super-horizon scale. The proof is made in the axion-comoving gauge. For a canonical mass, the axion pressure term causes deviation from the CDM only on scales smaller than the Solar System size. Beyond such a small scale the equations of the axion fluid are the same as the ones of the CDM based on the CDM-comoving gauge which are exactly identical to the Newtonian equations to the second order. Our analysis includes the cosmological constant, and can be easily applicable for the realistic situation including other fluids and fields.

Speaker: Hyerim Noh (Korea Astronomy and Space Science Institute)

18:36 Indirect Dark Matter searches with the ASTRI mini-array in the framework of the Cherenkov Telescope Array

Nowadays there are compelling evidences at several astrophysical scales for a large (~85%), dark, non-baryonic and non-relativistic component of the matter density of the Universe. The quest to explain the nature of Dark Matter (DM) represents a paramount issue of modern fundamental physics and astrophysics. The non-baryonic DM is compatible with a gas of cold and weakly interacting massive particles (WIMPs) expected to have a mass in the range between O(10)GeV and O(100)TeV. One of the most promising approaches to shed light on WIMPs is to search for signatures of DM annihilation/decay into Standar Model particles from regions of the sky believed to be highly DM dominated, such as the Galactic Centre, clusters of galaxies, and dwarf spheroidal galaxies (dSphs) of the Milky Way. Among final DM annihilation/decay states, a flux of gamma rays tracing back to astrophysical sources is expected at energies up to the DM mass, which could be accessible by Imaging Atmospheric Cherenkov Telescopes (IACTs). In this contribution, we present prospects on indirect DM searches from different optimal targets in the TeV mass region with the ASTRI mini-array, a Cherenkov Telescope Array's (CTA) precursor, composed of nine ASTRI small-sized, dual-mirror telescopes and proposed to be installed at the CTA southern site.

Speaker: Dr Saverio Lombardi (OAR-INAF, ASDC)

05_1836_Lombardi_ASTRI_DM_DEFINITIVE.pdf

18:39 Quantum vacuum as the cause of the phenomena usually attributed to dark matter

We show that if quantum vacuum fluctuations are virtual gravitational dipoles, then the phenomena usually attributed to hypothetical dark matter, may be considered as a consequence of the gravitational polarization of the quantum vacuum by the immersed baryonic matter; apparently, at least mathematically, the galactic halo of dark matter can be replaced by the halo of the polarized quantum vacuum.The eventual gravitational effects of the quantum vacuum "enriched" with virtual gravitational dipoles, can be revealed by the study of orbits of tiny satellites in trans-Neptunian binaries (for instance UX 25 and Eris-Dysnomia).

Speaker: Dragan Hajdukovic (Institute of Physics, Astrophysics and Cosmology (ME))

DarkMatter-Hajdukovic.pdf

DM-Hajduk.proc.pdf

18:42 Warm dark matter cosmological structures - from collapse to caustics and cores

Using cosmological simulations we explore the effects of warm dark matter (WDM) particles (e.g. sterile neutrinos)on the structure formation for different mass particles. Properties like the velocity dispersion and the damping of the fluctuation spectrum imprint a distinct signature on the structure formation mechanism as well as on the evolution of structures and on the internal structure of halos. Although the properties of the warm dark matter particles are strongly model dependent, we find that the structure formation mechanism is qualitatively more complex than originally assumed, a hybrid between top-down collapse and bottom-up growth. Comparing warm dark matter simulations with cold dark matter ones, we see that the internal structure of halos is also qualitatively different in these two cases. These effects and the differences between warm and cold dark matter can be tested with observations on both large scales and small scales. Finally we address some technical aspects in simulating warm dark matter.

Speaker: Sinziana Paduroiu (University of Geneva)

sinziana.paduroiu.poster.pdf

sinziana.paduroiu.talk.pdf

16:15 → 18:45 14 - Disks and jets

Convener: Thierry Courvoisier (University of Geneva)

16:15 Black Hole Jets from MRI-Generated Magnetic Fields

We propose a scenario for launching relativistic jets from rotating black holes, in which small-scale magnetic flux loops, sustained by disc turbulence, are forced to inflate and open by differential rotation between the black hole and the accretion flow. This mechanism does not require a large-scale net magnetic flux in the accreting plasma, whose presence in the environment of the central engine is questionable in many jet sources. Estimates suggest that the process could operate effectively for a wide range of systems, and particularly naturally and efficiently when the accretion flow is retrograde. We present the results of general-relativistic force-free electrodynamic simulations demonstrating the time evolution of the black hole's magnetosphere, the cyclic formation of jets, and the effect of magnetic reconnection. The jets are highly variable on timescales $\sim 10$-$10^3\, r_{\rm g}/c$, where $r_{\rm g}$ is the black hole's gravitational radius. The reconnecting current sheets observed in the simulations may be responsible for the hard X-ray emission from accreting black holes.

Speaker: Dr Kyle Parfrey (Lawrence Berkeley National Laboratory)

14_1615_Parfrey_BlackHole_Jets.key

14_1615_Parfrey_BlackHole_Jets.pdf

16:36 New connection between plasma conditions near black hole event horizons and outflow properties

Accreting black holes are responsible for producing the fastest, most powerful outflows of matter in the Universe. The formation process of powerful jets close to black holes is poorly understood, and the conditions leading to jet formation are currently hotly debated. In this talk I will present recent results that show empirical correlation between the properties of the plasma close to the black hole and the particle acceleration properties within jets launched from the central regions of accreting stellar-mass and supermassive black holes. In these sources the emission of the plasma near the black hole is characterized by a power law at X-ray energies during times when the jets are produced. We find that the photon index of this power law, which gives information on the underlying particle distribution, correlates with the characteristic break frequency in the jet spectrum, which is dependent on magnetohydrodynamical processes in the outflow. The observed range in break frequencies varies by five orders of magnitude, in sources that span nine orders of magnitude in black hole mass, revealing a similarity of jet properties over a large range of black hole masses powering these jets. This correlation demonstrates that the internal properties of the jet rely most critically on the conditions of the plasma close to the black hole, rather than other parameters such as the black hole mass or spin, and will provide a benchmark that should be reproduced by the jet formation models.

Speaker: Karri Koljonen (New York University Abu Dhabi)

Texas_Symposium_2015_Koljonen.pdf

16:56 Jets and winds from super-critical accreting black holes

Determining the power output and efficiency of accreting black holes is a fundamental astrophysical problem: we want to know the relation between mass accretion rate, radiative output (photons) and mechanical output (kinetic energy of jets and winds). We focus in particular on off-nuclear black holes that are accreting from a donor star at a rate near or above the critical Eddington limit. Many of them appear as "ultraluminous X-ray sources", evidence of their high radiative output. But how much additional power is carried by winds and jets? To answer this question, we studied a sample of powerful black holes associated with large bubbles of shock-ionized and/or photo-ionized gas. We used the bubbles as calorimeters to measure the power injected by the black hole into its surroundings. We find that black holes at super-Eddington accretion rates can have a mechanical power comparable to their radiative luminosity. Our study provides empirical constraints for theoretical models of super-Eddington accretion, and for models of black hole feedback in the early universe.

Speaker: Dr Roberto Soria (ICRAR-Curtin University)

rsoria_geneva_15b.pdf

rsoria_geneva_15b.pptx

17:17 Real-Time Evolution Of Relativistic Jets In Microquasars

Jets appear in Astrophysics in very different environments and scales across the Universe, and they seem to share common features in all cases. Their study can then help us to understand a widespread outflow mechanism. However, their large-scale dynamics remain hidden to observation along human time scales because they usually develop too slowly, either because of their large sizes (in active galactic nuclei), or because of their slow velocities (in Herbie-Haro objects). However, microquasars combine both relatively short extensions and relativistic velocities, giving us the chance to better study the jet evolution and interaction with their environments in almost real time. Here we present, for the first time, an observational proof of such large-scale morphological changes in the case of GRS 1758-258. Archival radio observations have been used to conform a set of photograms of the evolution of such microquasar throughout two decades, confirming its structural variations that may be related to hydrodynamical instabilities. In addition, we have studied the prototypical microquasar 1E 1740.7-2942 in radio wavelengths to find out again changes in the jet morphology, that seem to be mainly originated by precession in this case. These results let us to confirm their up-to-now disputed Galactic nature and provide a benchmark for testing theoretical models accounting for relativistic jets dynamics and their interactions with the medium.

Speaker: Dr Pedro Luis Luque-Escamilla (Universidad de Jaén)

14_1717_Luque_Escamilla_Real-Time_Evolution_Of_Relativistic_Jets_In_Microquasars.pdf

14_1717_Luque_Escamilla_Real-Time_Evolution_Of_Relativistic_Jets_In_Microquasars.pptx

17:38 Rapid variations of polarisation in X-ray binaries

Recently, evidence for synchrotron emission in both black hole and neutron star X-ray binaries has been mounting, from optical/infrared spectral, polarimetric, and (possibly) fast timing signatures. Time-resolved optical and infrared polarimetric observations of X-ray binaries are presented. It is found that the infrared emission of GX 339-4 in the hard state contains variable polarization on timescales of < 60 seconds. In the first study of its kind, we present strictly simultaneous time-series X-ray, UV, optical, infrared polarimetry and radio observations of Cygnus X-2. Variability in the flux is tested for cross-correlations with all other wavelengths, and polarisation strength and angle is cross-correlated with flux variability. Correlated variability could be caused by a disc-jet coupling mechanism on short timescales. The results are compared to other neutron star XRBs such as Sco X-1, which also has a variable polarisation signature at optical/infrared wavelengths. The synchrotron emission of jets can be highly linearly polarised, depending on the configuration of the magnetic field, and the magnetic fields near the jet base in these systems appear to be turbulent, variable and aligned with the jet axis. This probes the physical conditions in the accretion (out)flow and demonstrates a new way of connecting inflow and outflow, using both rapid timing and polarisation. The implications for future measurements of X-ray polarisation are discussed. We also present a detection of polarisation in the quiescent black hole system Swift J1357.2- 0933 which originates from its highly variable infrared emission. These results likely constrain the magnetic structure in the inner regions of the jets launched from accreting X-ray binaries.

Speaker: Dave Russell

14_1738_Russel_Rapid_variations_of_polarisation_in_X-ray_binaries.pdf

14_1738_Russel_Rapid_variations_of_polarisation_in_X-ray_binaries.ppt

17:59 Stability of relativistic two-component jets

Several observations of astrophysical jets show evidence of a structure in the direction perpendicular to the jet axis, leading to the development of “spine & sheath” models of jets. Two-component jets have been already examined (e.g. Meliani & Keppens 2007, Meliani & Keppens 2009) for relativistic hydrodynamic jets and relativistic magnetized jets with poloidal magnetic field. These studies focused on a two-component jet consisting of a highly relativistic inner jet and a slower - but still relativistic - outer jet surrounded by an unmagnetized environment. These jets were susceptible to a relativistic Rayleigh-Taylor-type instability, depending on the effective inertia ratio of the two components. This work is now extended by taking into account the presence of a non-zero toroidal magnetic field. We examine analytically the stability of this configuration and also perform numerical simulations, using MPI-AMRVAC, to compare with the previously studied cases. Depending on the configuration, the toroidal magnetic field might stabilize the previously mentioned case or trigger instabilities on a different time scale. Furthermore, the introduction of a toroidal magnetic field component allows examining different types of relativistic jets (Poynting dominated or matter dominated) by modifying the magnetization parameter. Thus, we can investigate different combinations of matter/ Poynting dominated two-component that will end up (un)stable.

Speaker: Mr Dimitrios Millas (KU LEUVEN)

Millas_Stability_of_Relativistic_Two_Component_Jets.pdf

Millas_Stability_of_Relativistic_Two_Component_Jets.ppt

movieproperdens.avi

proc_Millas_Texas2015.pdf

18:19 The Blandford-Znajek theory revisited

How powerful relativistic jets are generated is still one of the most important topics of the modern astrophysics. One of the most interesting and adopted theories was developed by Blandford and Znajek in 1977 with reference to jets from black holes. In the present work, I would like to draw the attention on some relatively unexplored features of the theory, with particular reference to the analogies with electromagnetic generators.

Speaker: Dr Luigi Foschini (National Institute for Astrophysics - INAF)

Foschini_posterFull.pdf

proc_foschini_poster.pdf

18:22 Evolution of luminosity-linearsize relation for sources with steep radio spectrum

We consider four samples of steep-spectrum radio sources from our catalogue UTR-2 at the decameter band. These contain galaxies and quasars of both spectral types - with linear steep spectrum and break steep spectrum. To obtain the relation of low-frequency luminosity, at the frequency 25 MHz, L_25 and linear size R of sample objects we determine one at the different redshift ranges at the frame of LambdaCDM Universe model. The derived relatios show positive power trend (L_25 ~ R^n, n = 0.5....2.0) for galaxies and quasars. Since the object's luminosity ratio for monochromatic luminosities at different frequency ranges is independent from the Universe model, one is examined on the luminosity ratio-linear size relation. For the purpose of estimate on the linear size's cosmological evolution, we determine linear size-redshift relations at the narrow luminosity bins (R ~ (1+z)^k, k = 0.7....1.87) in our samples. It is very interesting, that obtained luminosity ratio-linear size relations at higher frequency ranges (infrared, X-ray) display two branches of evolution of steep-spectrum radio sources.

Speaker: Dr Alla Miroshnichenko (Institute of Radio Astronomy, NAS of Ukraine)

Mirosh-Geneva-15_pres.pdf

Mirosh-Geneva-15_pres.ppt

Poster_Miroshnichenko_Geneva_Symp2015.pdf

Poster_Miroshnichenko_Geneva_Symp2015.ppt

18:25 gap

16:15 → 18:45 15 - Binaries: Millisecond pulsars

Convener: Alessandro Papitto

16:15 Formation of millisecond pulsars and double neutron stars

Radio millisecond pulsars (MSPs) have been spun-up to very high rotation frequencies via accretion of mass and angular momentum from a companion star in a binary system. In this talk, I will review the formation of MSPs and discuss recent observational and theoretical challenges in understanding their formation and evolution via the standard recycling scenario. I will discuss MSP properties like spin periods, masses and orbital characteristics, and also briefly discuss new developments related to our understanding of the formation of double neutron star systems.

Speaker: Thomas Tauris (Uni. Bonn)

15_1615_Tauris_Formation_of_millisecond_PUBLIC_ONLINE.pdf

16:45 Accretion and rotation power in ms pulsars

Neutron stars in low mass X-ray binaries can be spun-up to millisecond rotational periods by accreting the matter transferred by a companion star. When the rate of mass transfer decreases at the end of this Gyr-long X-ray bright phase, a radio pulsar powered by the rotation of the neutron star magnetic field turns on. Recently, the evolutionary link between these two classes of sources was finally proven by the XMM-Newton discovery of a millisecond pulsar observed to swing between accretion (X-ray bright) and rotation (radio bright) pulsar behaviour. This source is the prototype of a new class of transitional systems that alternate between accretion and rotation-powered states in response to variations of the rate of mass in-flow, on time scales as short as a couple of weeks. Observations of this and other similar systems indicate that transitions to the accretion phase not only involve bright X-ray outbursts, but also a fainter intermediate X-ray state, possibly caused by centrifugal inhibition of the matter in-fall. I will summarize the main observed properties, as well as prospects of finding more sources of this newly established class.

Speaker: Dr Alessandro Papitto (Space Science Institute Barcelona (ICE) CSIC-IEEC)

15_1645_Papitto_accretion_and_rotation.pdf

17:10 The peculiar X-ray variability of the transitional pulsar IGR J18245-2452

The pulsar IGR J18245$-$2452 was dubbed as transitional, after detection of X-ray accretion induced pulsations, during an outburst which interrupted radio, rotationally-powered emission. The source was observed at the peak of its X-ray flux using XMM-Newton twice for a total exposure of 90 ks. At odds with other accreting millisecond pulsars, its power spectrum is characterised by a strong flicker noise with no measurable low-frequency cutoff and very weak additional band-limited noise (Ferrigno et al., 2014). The count-rate changes by two orders of magnitudes in time intervals as short as a few second, and the spectra are luminosity dependent. Moreover there are episodes of spectral hardening during the lower-flux periods. This might be indicative of the onset of mass ejection from the inner disk boundary with variable intensity, know as weak and strong propeller. Theoretical and numerical modelling of disk-magnetospheric interaction predicts that when this effect takes place, the accretion-induced luminosity might present transient quasi-periodic behaviour due to the accumulation of matter at the magnetospheric boundary and its subsequent accretion. In this contribution, we present the rich phenomenology of this still unique object and the similarities with other objects of the same class. We will then focus on our search for transient quasi-periodic signals using different techniques such as dynamical power spectra and wavelet analysis. We compare our results with the output of models in which matter is ejected from the disk by the interaction with the neutron star's magnetic field and it is partially recycled at an outer radius. This might induce a variable accretion rate responsible of the strong flares and dips in the light curve with an apparent stochastic behaviour.

Speaker: Carlo Ferrigno (University of Geneva)

15_1710_Ferrigno_The peculiar xray variability.key

15_1710_Ferrigno_The_peculiar_xray_variability.pdf

17:30 Simulations of the Magnetospheres of Accreting Millisecond Pulsars: Torque Enhancement, Spin Equilibrium, and Jet Power

The interaction of a rotating star's magnetic field with a surrounding plasma disc lies at the heart of many questions posed by neutron stars in X-ray binaries. I will present global simulations of this interaction, performed in the force-free (high-magnetization) limit of relativistic MHD, showing the opening of magnetic field lines, the formation and reconnection of magnetospheric current sheets, and a substantial increase in the spin-down torque applied to the star by the pulsar wind. When the disc conductivity is high, the principal simulation results can be captured in a simple analytic model for the disc-opened flux, the torques exerted on the star by the magnetosphere, and the power extracted by the electromagnetic wind. Using this model, I will describe the conditions under which the system enters an equilibrium spin state, in which the accretion torque is instantaneously balanced by the pulsar wind torque alone. For magnetic moments, spin frequencies, and accretion rates relevant to accreting millisecond pulsars, the spin-down torque from this enhanced pulsar wind can be substantially larger than that predicted by existing models of the disc-magnetosphere interaction, and is in principle capable of maintaining spin equilibrium at frequencies less than 1 kHz. This mechanism may account for the non-detection of frequency increases during outbursts of SAX J1808.4-3658 and XTE J1814-338, and may be generally responsible for preventing spin-up to sub-millisecond periods. If the pulsar wind is collimated by the surrounding environment, the resulting jet can satisfy the power requirements of the highly relativistic outflows from Cir X-1 and Sco X-1. In this framework, the jet power scales relatively weakly with accretion rate, and would be suppressed at high accretion rates only if the stellar magnetic moment is sufficiently low; this may be consistent with the absence of soft-state jet quenching in some observed neutron-star X-ray binaries.

Speaker: Dr Kyle Parfrey (Lawrence Berkeley National Laboratory)

15_1730_Parfrey_Simulations of magnetosphere.key

15_1730_Parfrey_Simulations_of_magnetosphere.pdf

17:50 3FGL J1544.6-1125: radio imaging analysis of newest transitional millisecond pulsar

Recently, Bogdanov $\&$ Halpern (2015) identified the unassociated Fermi gamma-ray source $3$FGL~J$1544.6-1125$ as only the $4$th known "transitional millisecond pulsar" (tMSP), a claim further bolstered by follow-up observations by Bogdanov (2015). The tMSPs are a newly discovered class of binary systems that transition between states as a radio millisecond pulsar and a low-mass X-ray binary (LMXB). In the LMXB state tMSPs show X-ray variability over ~$10-100$s, switching between 'high' and 'low' luminosity modes, as well as infrequent 'flares'. In the high mode, coherent X-ray pulsations are seen, indicating channeled accretion onto the neutron star surface despite the very low accretion rate, and offering the potential to study very low-level accretion onto neutron stars. A coordinated radio/X-ray campaign undertaken for PSR J$1023+0038$ showed that this tMSP is much brighter in radio than expected, and with rapidly variable and flat spectrum continuum emission most likely associated with compact, self-absorbed jet (Deller et al. 2015). This strongly hints at radiatively inefficient accretion flow where majority of accretion energy goes into an outflow. $3$FGL J$1544.6-1125$ is currently the only other system in the right state for detailed observations to confirm whether efficient jet formation is common to all tMSPs, and would add a $4$th important data point to the newly hypothesized radio/X-ray luminosity relationship for tMSPs. We have therefore observed it with VLA four times over the period of several weeks. Preliminary results indeed show a behaviour similar to J$1023$, further strengthening the case for $3$FGL J$1544$ being a tMSP. I would be presenting results from this first ever observational campaign to detect the source in radio.

Speaker: amruta jaodand (ASTRON- Netherlands Institute for Radio Astronomy)

15_1750_Jaodand_3FGL1544.key

15_1750_Jaodand_3FGL1544.pdf

18:05 Orbitally Modulated High-Energy Emission from Black Widows and Redbacks

Searches of unidentified Fermi sources have vastly expanded the number of known galactic-field “black widow” and “redback” circular MSP binary systems. We model the high-energy emission from these systems due to relativistic leptons in the pulsar wind and those accelerated in intrabinary shocks. We show that the observed radio eclipses of the MSP can constrain the shock and system geometry. We also reproduce characteristic double-peaked orbitally modulated X-ray emission observed in many MSP binaries through Doppler boosting along the intrabinary shock. Redbacks and transitional pulsar systems, where the double-peaked X-ray light curve is observed at inferior conjunction, are suggested to be intrinsically different in shock geometry than other MSP binaries. Inverse Compton emission as a function of energy and orbital phase, from electrons in the pulsar wind or intrabinary shock scattering UV photons from the irradiated companion, is explored. The anticipated modulation of high-energy emission at the binary orbital period presents a unique astrophysical probe of the unknown physics of pulsar winds, relativistic shock acceleration and transport. Implications for Fermi-LAT and CTA target selection and searches are discussed.

Speaker: Dr Zorawar Wadiasingh (Centre for Space Research, North-West University)

15_1805_Wadiasingh_Orbitally_Modulated_HE_Emission.key

15_1805_Wadiasingh_Orbitally_Modulated_HE_Emission.pdf

18:20 On the low magnetic fields of millisecond pulsars

Millisecond pulsars (MSPs) are old and very fast rotating neutron stars (NS) with much weaker magnetic fields than the younger classical pulsars and magnetars. Most MSPs are in binary systems, suggesting a "recycling scenario", in which a classical pulsar accretes matter from its companion and as a consequence spins up. Although this scenario explains the fast rotation, it is not clear yet how the magnetic field is reduced. The standard scenarios attribute it to the accretion process, either by increasing the temperature and thus the resistivity of the crust, leading to dissipation of the currents (assumed to flow in the crust), or by diamagnetic screening of the field by the accreted matter (which is implausible, because of magnetic buoyancy and the stiffness of the magnetic field lines). We examine an alternative hypothesis, in which ambipolar diffusion expels the magnetic flux from the neutron star core, in this way driving its decay. This process is particularly effective during the long period in which the neutron star has cooled substantially and has not yet started accreting, making the final magnetic field dependent on the evolutionary time of the companion star (and thus its initial mass), and naturally yielding field strengths of the observed magnitudes. Our predictions also appear to be consistent with the observed distribution of magnetic fields of millisecond pulsars according to their companion type: He white dwarfs, CO white dwarfs, or neutron stars.

Speaker: Ms Marilyn Cruces (Instituto de Astrofísica, Pontificia Universidad Católica de Chile)

15_1820_cruces_on_the_low_magnetic_fields.key

15_1820_cruces_on_the_low_magnetic_fields.pdf

18:35 Using millisecond pulsars to calibrate XMM/Newton onboard clock

The XMM-Newton space telescope is capable of 30-microsecond time resolution but its onboard clock drifts, for example due to changes in temperature. Current calibration documentation only provides an upper limit on the clock drift of 10^-8, but observations of X-ray millisecond pulsars (MSPs) suggest that it should be more stable. Using kilo-second XMM-Newton observations of MSPs taken with the EPIC pn-camera in fast timing mode in addition to radio timing measurements from the ATNF pulsar catalog for J1939+2134 (641.9 Hz), J0437-4715 (173.6 Hz), J0218+4232 (430.4 Hz) and J0534+2200 (29.9 Hz), we analyzed the pulse shape for each object with the aim to detect the broadening in the profile produced for a linear clock drift through the use of the statistical H-test plus minimization methods. Our results suggest that the clock is much more stable than what was previously claimed in the literature. A well-established clock stability would permit to derive physical quantities with a properly understood accuracy and perform interesting measurements in accreting X-ray millisecond pulsars (e.g. spin-down rate), transients, among others.

Speaker: Ms Marilyn Cruces (Instituto de Astrofísica, Pontificia Universidad Católica de Chile)

15_1838_Cruces_using_millisecond_pulsar.key

15_1838_Cruces_using_millisecond_pulsar.pdf

18:38 gap

16:15 → 18:45 16 - Black holes

Convener: Didier Barret (IRAP (UPS/CNRS))

16:15 Rapid variability as a probe of warped space-time around accreting black holes

The geometry of the inner accretion flow of X-ray binaries is complex, with multiple regions contributing to the observed emission. Frequency-resolved spectroscopy is a powerful tool in breaking this spectral degeneracy. We have extracted the spectra of the strong low-frequency quasi-periodic oscillation (QPO) and its harmonic in GX339-4 and XTE J1550-564, and compare these to the time-averaged spectrum and the spectrum of the rapid (< 0.1s) variability. Our results support the picture where the QPO arises from vertical (Lense-Thirring) precession of an inhomogeneous hot flow, softer at larger radii closer to the truncated disc and harder in the innermost parts where the rapid variability is produced. This coupling between variability and spectra allows us to constrain the soft Comptonization component, breaking the degeneracy plaguing the time-averaged spectrum and revealing the geometry of the accretion flow close to the black hole.

Speaker: Magnus Axelsson

axelsson_texas2015_xrb.key

axelsson_texas2015_xrb.pdf

16:35 Approximation of relevant elliptical equations in the Schwarzschild metric and some astrophysical applications

In this talk I consider the light path of observed photons emitted by matter in a *Schwarzschild gravitational field*. *Ray-tracing methods* are employed to tackle this problem and the used main equations are: **light bending**, **time delay** and **solid angle**. They are expressed through *elliptic integrals* that can be resolved numerically through generally complex routines. To run faster codes and to deal more easily with the applications *Beloborodov (2002)* and *Poutanen & Beloborodov (2006)* found a simple polynomial approximation to describe respectively light bending and time delay with high-accuracy for photon emitted at radius out of the event horizon ($r\gt r_S=2GM/c^2$). Though the results are relevant, it appears not clear how to derive them. I propose a *mathematical method* able to recover the above equations and in addition to provide an analytical approximation, for the first time, of the solid angle equation. Some applications show the power of this set of approximation equations like iron line profile and polarized light coming from an accretion disk.

Speaker: Vittorio De Falco (University of Basel)

Presentation - Vittorio De Falco.pdf

16:55 Frame dragging, unipolar induction and Kerr black hole magnetospheres

Making use of $3+1$ formulation of black hole electrodynamics, it is argued that the frame-dragging effect combines with unipolar induction, to sustain the double-structured magnetosphere consisting of the outer and inner domains, and high-energy activities therein. The emf's, $\cal{E}_{\rm out}$ and $\cal{E}_{\rm in}$, of a pair of unipolar induction batteries driving electric currents in the two domains are equivalent to those due to a pair of magnetized rotators spinning anti-parallelly each other with $\Omega_{\rm F}$ and $-(\Omega_{\rm H}-\Omega_{\rm F})$, located back-to-back at both sides of the interface S$_{\rm N}$ at $\omega=\Omega_{\rm F}$ in-between, where $\Omega_{\rm F}$, $\Omega_{\rm H}$ and $\omega$ are the angular velocities of field lines, the Kerr hole and the frame dragging due to the hole's spin. The difference, $\cal{E}_{\rm out}-\cal{E}_{\rm in}$$=\Delta V=- (\Omega_{\rm H}/2\pi c)\Delta\Psi$, corresponding to the difference of the two angular velocities of hypothetical rotators at S$_{\rm N}$, $\Omega_{\rm F}-[-(\Omega_{\rm H}-\Omega_{\rm F}])=\Omega_{\rm H}$, will provide a voltage drop strong enough to develop a magnetized gap in which pair-creation discharges will take place to provide copious charged particles to out- and in-flows in both domains and allow field lines pinned down to fix $\Omega_{\rm F}$ with the local frame-dragging angular velocity, i.e., $\Omega_{\rm F}=\omega_{\rm N}$. Such a situation will allow one to present the hole's double structure in terms of a twin-pulsar model, consisting of a pulsar-type wind flowing toward infinity and an anti-pulsar-type wind flowing in toward the horizon, with the common particle/current sources where field lines are pinned down (see I. Okamoto, PASJ, 2015, 67, 69)

Speaker: Prof. Isao Okamoto (National Astronomical Observatory of Japan)

proceedings-Okamoto.pdf

viewgraphs-Okamoto.pdf

17:15 Gaps in black holes magnetospheres

We consider the possible existence and observational consequences of the so-called vacuum "gaps" in the SMBH force-free magnetospheres in RIAF type sources. The gaps are the sites with a lack of the volume charge density in comparison to the plasma-filled force-free regions of the magnetosphere. They are analogous to the gaps in the pulsars magnetospheres. In such gaps direct acceleration of charged particles by unscreened electric field could occur. It is vacuum gaps that could play an important role in the process of the plasma filling of the BH magnetosphere and because of the direct particle acceleration are also interesting from the point of view of the UHECR origin problem. We analyse the gap properties by numerical modelling of the particle acceleration and radiation in the black hole magnetosphere, embedded into the accretion flows' background radiation field. We show that for the some range of the RIAF parameters there are sharp features in the radiation spectrum at GeV-TeV energies, produced by the particles, accelerated in the gaps. The observation of these features would allow to verify the discussed model.

Speaker: Ksenia Ptitsyna (INR Moscow, MSU Moscow, ISDC Geneve)

TeXas-Ptitsyna.pdf

17:18 Can Black Holes Be Accelerators of Spinning Massive Particles?

It is a well known effect that a rotating black hole can accelerate spinless particles to in principle arbitrary energies. Within the formalism of the Spinning Top it is investigated to which extend the "corresponding" process is also possible: *"Can spinning tops be accelerated by a non-rotating black hole?"* It is found that this is indeed the case.

Speaker: Prof. Benjamin Koch (Pontifica Universidad Catolica de Chile)

BenjaminKoch-Texas-2015.pdf

17:21 Comments on the Effect of Frame Dragging

In this study, accurate and detailed solution of the frame-dragging process has been presented with a newly deduced equation of motion. Numerical solutions show that the results obtained in this study are somewhat different than those results presented in Thirring (1918). Obtained results have been applied to various astrophysical mediums as case studies.

Speakers: Kadri Yakut (University of EGE), ismail özbakır

proc_I_OZBAKIR.pdf

17:24 Hawking radiation cannot exist if quantum vacuum fluctuations are gravitational dipoles

While it is neglected, Hawking radiation is model-dependent; it depends on our model of the quantum vacuum. It was recently suggested that what we call dark matter and dark energy can be explained as the local and global effects of the gravitational polarization of the quantum vacuum by the immersed Standard Model matter. This result appears as the consequence of the working hypothesis that by their nature quantum vacuum fluctuations are virtual gravitational dipoles. Here, as a consequence of the same hypothesis we argue that instead of the nonexistent thermal Hawking radiation there is a much stronger non-thermal radiation which is caused by the conversion of virtual particle-antiparticle pairs into real ones; this conversion happens deep inside the horizon. Contrary to Hawking radiation which leads to the black hole information paradox, there is no information loss paradox within the framework of the quantum vacuum “enriched” with virtual gravitational dipoles.

Speaker: Dragan Hajdukovic (Institute of Physics, Astrophysics and Cosmology (ME))

HawkingRadiation-Hajdukovic.pdf

HR-Hajduk.proc.pdf

17:27 gap

16:15 → 18:45 11 - Gravitational waves

Convener: Chiara Caprini (CEA-Saclay)

16:15 Late-time cosmology with eLISA

In this talk I will consider the application of eLISA as a probe of the late-time cosmological expansion. In particular I will first review the concept of standard sirens and how these can be used to investigate the distant-to-redshift relation. I will then discuss the best strategies to obtain as many standard sirens as possible, taking into account what kinds of electro-magnetic counterparts could reasonably be detected and by which instruments. Finally, employing realistically simulated data, I will present the constraints we will be able to obtain on the cosmological parameters of LambdaCDM and dark energy models.

Speaker: Nicola Tamanini (CEA - France)

Late-time cosmology with eLISA

16:35 Electromagnetic Emission from Compact Supermassive Black Hole Binaries

In this talk, I will discuss possible characteristics of electromagnetic (EM) emission from supermassive black hole (SMBH) binaries. In particular, any detectable EM emission is likely to be time-variable, and contain unique spectral signatures, which should aid identifying SMHB binaries. I will discuss recent hydrodynamical simulations, which suggest quasiperiodic modulations in the accretion rate onto the BHs prior to coalescence. These time-variable EM signatures may be used to identify unique counterparts of gravitational wave sources expected to be detected by (e)LISA and by Pulsar Timing Arrays, or to discover binary SMBHs in time-domain EM surveys. As an example of the latter, the quasar PG1302 was recently discovered to have a 5-yr periodic optical variability. I will comment on the interpretation of this quasar as a SMBH binary candidate and its implications.

Speaker: Prof. Zoltan Haiman (Columbia University)

HaimanGeneva2015.pdf

haiman.pdf

16:55 The fate of Super Massive Black Holes in galaxy mergers

We study numerically the fate of SMBHs in galaxy mergers. If the galaxies involved in these mergers have a gas fraction of at least %1 is expected that a massive gaseous disk with a mass of ten to hundred times the mass of the SMBHs will be formed in the central kilo parsec of the merger remnant. The SMBHs in these nuclear region will form a SMBH binary which separation will shrink mainly due to the gravitational torque produced by the gaseous disk. We focus our study in the transport of angular momentum from the binary to the disk and how this transport can result on the formation of a gap in the gaseous disk. If the formation of such gap occurs the shrinking of the SMBH binary will be dramatically delayed, instead if the binary doesn't excavate a gap on the disk the shrinking of the binary will continue until the extraction of angular momentum due to the emission of gravitational waves becomes efficient enough to drive the final coalescence of the binary. We find in all our simulations of galaxy mergers that the formation of such a gap is unlikely and will be possible only if the SMBH binary mass is comparable or much greater than the mass of the gaseous disk. Our simulations imply that the mass of the SMBHs must be at least of the order of $10^{10}$ M$_{\odot}$, which is larger than the mass of the most massive SMBHs harbour by giant elliptical galaxies or cD galaxies. Our results have important implication on the number of SMBHs that will experience a fast migration and will enter in the gravitational wave emission regime, estimation that it is crucial to determine the amount of gravitational waves that we expect to observe with the future mission eLISA.

Speaker: Prof. Andres Escala (Universidad de Chile)

11_1655_Escala_ThefateOfSuperMassiveBlackHoles.pdf

11_1655_Escala_ThefateOfSuperMassiveBlackHoles.ppt

17:15 The underlying simplicity of precessing black-hole binaries

Modelling the inspiral, merger and ringdown of generic (i.e., precessing) black-hole binaries has long been a major challenge for theoretical gravitational-wave astronomy. I will present a simple picture of the underlying phenomenology of these systems, which has lead to a novel technique to produce accurate generic waveform models.

Speaker: Mark Hannam (Cardiff University)

11_1715_Hannam_The_underlying_simplicity.pdf

17:35 Accurate Phenomenological Waveform Models for Black Hole Coalescence in the Frequency Domain

This talk will discuss the current state of the phenomenological waveform approach for non-precessing black hole binaries, and recent numerical relativity simulations used in the modelling and performed with the BAM code. Using these simulations, we have extended the calibration range of our inspiral-merger-ringdown model to mass ratio 18. The talk will in particular also discuss the anatomy of the merger-ringdown waveform in the frequency domain, and the construction of hybrid post-Newtonian-numerical relativity waveforms.

Speaker: Sascha Husa

11_1735_Husa_Accurate_phenomenological_waveform.key

11_1735_Husa_Accurate_phenomenological_waveform.pdf

17:55 Gravitational waveform from binary neutron star mergers: Numerical relativity and Effective-one body

Measuring the neutron-star equation of state with gravitational waves is one of the scientific goal of grand-based gravitational-wave laser interferometers. To achieve this, we need end-to-end waveforms of binary neutron star mergers. Here we present waveforms that are computed with a long-term numerical relativity simulation. Then the waveforms are compared with those computed with effective one body formalism including the tidal effect. We construct hybrid waveforms of binary neutron star mergers from 100Hz to 2000Hz. We discuss measurabilities of the equation of state with these hybrid waveforms.

Speaker: Kenta Hotokezaka (Hebrew University)

11_1755_Hotokezaka_GWfromBinaryNeutronStarMerges.pdf

18:15 Gravitational Wave Signals from 3D Neutrino Simulations of Core-Collapse Supernovae Hydrodynamics

To this day the exact nature of the detonation mechanise in core collapse supernovae reminds somewhat of a mystery. While numerical models are becoming more and more sophisticated, observations of the inner engine remain elusive. Because he core surrounded by dens stellar matter, electromagnetic radiation can only provide indirect information. Neutrinos and gravitational waves on the other hand can propagate almost unhindered thought the stellar material. For the last decade, or so, supernova modellers have predicted gravitational wave signatures based on their simulations. I will follow in these footsteps and present a detailed analysis of the gravitational wave signal during the post-bounce phase, from the latest core collapse simulations. I present the signal arising from sophisticated three-dimensional simulations of three progenitors. The theoretical signal from our simulations consists of two distinct features: One emission component below 250 Hz associated with the standing accretion shock instability and a one component above 300 Hz associated mainly with convection deep within the forming neutron star. The former component arises from both the proto-neutron star exterior and interior.

Speaker: Haakon Andresen (Max Planck Institut für Astrophysik)

11_1815_Andresen_Gravitational_Waves_signal.pdf

18:35 gap

16:15 → 18:45 10 - Cosmic magnetic fields: origin, evolution and signatures

Convener: Tina Kahniashvili

16:15 Novel Approaches for the Analysis of Extragalactic Magnetic Fields

In order to give a consistent picture of cosmic, i.e. galactic and extragalactic, magnetic fields, different approaches are possible and often even necessary. Here we present three of them: First, a semianalytic analysis of the time evolution of primordial magnetic fields from which their properties and, subsequently, the nature of present-day intergalactic magnetic fields may be deduced. Second, the use of high-performance computing infrastructure by developing powerful algorithms for (magneto-)hydrodynamic simulations and applying them to astrophysical problems. We are currently developing a code which applies kinetic schemes in massive parallel computing on high performance multiprocessor systems in a new way to calculate both hydro- and electrodynamic quantities. Finally, as a third approach, astroparticle physics might be used as magnetic fields leave imprints of their properties on charged particles transversing them. Here we focus on electromagnetic cascades by developing a software based on CRPropa which simulates the propagation of particles from such cascades through the intergalactic medium in three dimensions. This may in particular be used to obtain information about the helicity of extragalactic magnetic fields.

Speaker: Dr Andrey Saveliev (University of Hamburg/Keldysh Institute)

Saveliev_Geneva.pdf

Saveliev_Geneva_proc.pdf

16:35 Self-similar magnetic, turbulent and thermal energy evolution in massive galaxy clusters

Massive galaxy clusters (GC) are filled with a hot, turbulent and magnetised intra-cluster medium (ICM). They are still forming under the action of gravitational instability driving supersonic accretion flows, which partially dissipate into heat through a complex network of large scale shocks, while partly excite giant turbulent eddies and cascade. Amongst others turbulence amplifies magnetic energy by way of dynamo action. This pattern of gravitational energy turning kinetic, thermal, turbulent and magnetic is a basic feature of GC hydrodynamics but quantitative modelling remains a challenge. In this contribution we present results from recent high resolution numerical simulations of structure formation in which the time dependent turbulent motions of the intracluster medium of a massive galaxy cluster are resolved and their statistical properties quantified for the first time. Combined with independent state-of-theart results on turbulent dynamo we determine without adjustable parameters the thermal, turbulent and magnetic history of giant GC. I will discuss the scale free character of energy structure in the intracluster medium and how it encodes information about the efficiency of turbulent heating and dynamo action directly accessible through astronomical observations.

Speaker: Dr Francesco Miniati (ETHZ - ETH Zurich)

10_1635_Miniati_Self-similar_magnetic_turbulent.key

10_1635_Miniati_Self-similar_magnetic_turbulent.pdf

16:55 The Chiral Magnetic Effect and its Role in Astrophysics and Cosmology

We will present work on the chiral magnetic instability in the context of hot neutron stars and its possible role for magneto genesis in the early Universe. Whether a chiral asymmetry in the electron sector, induced for example by the electroweak interaction, leads to growing helical magnetic fields depends on many factors that will be discussed in this talk.

Speaker: Guenter Sigl (II. Institut für theoretische Physik, Universität Hamburg)

texas-sigl.pdf

17:15 Galactic magnetic field and uncon-ventional cosmic ray propagation

Fermi-LAT, PAMELA, AMS-02, Planck and IceCube are providing us with impressive multimessenger pictures of our Galaxy. The diffuse components of those emissions are commonly modeled assuming uniform cosmic ray (CR) transport properties. Such an approach, however, is not motivated neither by theoretical nor observational arguments. I will show that relaxing the uniform CR propagation assumption it allows to explain several anomalies including the excess of gamma-rays observed by Milagro and Fermi-LAT in the inner Galactic plane and part of the high-energy neutrino emission measured by IceCube. I will argue as such a behaviour may be explained under quite reasonable conditions of the regular and turbulent components of the Galactic magnetic field.

Speaker: Dario Grasso (INFN)

10_1715_Grasso_galactic_magnetic_field.pdf

17:35 gap

16:15 → 18:45 19 - VHE & CR: VHE observations

Convener: Elisa Prandini (Universite de Geneve (CH))

16:15 Extragalactic science with the Cherenkov Telescope Array

The Cherenkov Telescope Array (CTA) is the next-generation observatory for ground-based gamma-ray astronomy. A Key Science Program (KSP) of observations will be conducted, providing legacy data sets of benefit to the entire astronomical community. This contribution presents the extra-galactic science addressed in the CTA KSP. The objectives contain targeted observations of active galactic nuclei, galaxy clusters and star-forming galaxies as well as follow-up observations of gamma-ray bursts and other transients triggered by multi-messenger alerts. The KSP also includes a survey of one quarter of the extra-galactic sky, permitting a thorough search for cosmic particle accelerators and the exploration of the unknown.

Speaker: Lucie Gerard

EGAL_KSP_CTA.pdf

16:40 The SST-1M Project of the Cherenkov Telescope Array: Status and Physics Perspectives

The SST-1M telescope is one of the prototypes under construction proposed to be part of the future Cherenkov Telescope Array. It uses a standard Davis-Cotton design for the optics and telescope structure, with a dish diameter of 4 meters and a large field-of-view of 9 degrees. An innovative camera with Silicon Photomultipliers and fully digital readout and trigger electronics, DigiCam, has been designed and its first prototype will be installed on the existing telescope structure in 2016. In this contribution we give a general overview of the project status. The key existing performance results and commissioning data will be briefly presented while the emphasis will be put on the science case of the SST telescopes in the framework of the Cherenkov Telescope Array. Main target of these small telescopes is to investigate the very high energy sky above few TeV with unprecedented sensitivity, making them the ideal probe of hadronic mechanisms in galactic sources and Pevatrons. Moreover, the large field of view will allow to perform wide surveys and improve dark matter searches.

Speaker: Matthieu Heller (Universite de Geneve (CH))

CTA_SST1M_TexasSymposium_Heller.key

CTA_SST1M_TexasSymposium_Heller.pdf

17:00 ASTRI SST-2M prototype and ASTRI mini-array data analysis and scientific prospects in the framework of the Cherenkov Telescope Array

In the framework of the international Cherenkov Telescope Array (CTA) observatory, the Italian National Institute for Astrophysics (INAF) is developing the ASTRI SST-2M end-to-end prototype, installed at Mt. Etna (Italy) on September 2014, and is leading, in collaboration with Universities from Brazil and South Africa, the ASTRI mini-array composed of nine ASTRI small-sized, dual-mirror telescopes and proposed to be installed at the CTA southern site. The project is also including the full data handling chain from raw data up to final scientific products, and a dedicated software for data reduction and scientific analysis is under development for both the ASTRI SST-2M prototype and the ASTRI mini-array, in compliance with the CTA requirements. In this contribution, we discuss in detail the outcome of the developed scientific analysis on both ASTRI prototype and mini-array simulated data, in order to provide information on the expected sensitivities and to introduce the main scientific prospects for the mini-array.

Speaker: Dr Saverio Lombardi (OAR-INAF, ASDC)

19_1700_Lombardi_ASTRI_ANALYSIS_AND_SCIENCE_DEFINITIVE.pdf

proc_Lombardi_ASTRI_ANALYSIS_AND_SCIENCE_DEFINITIVE.pdf

17:20 Multiwavelength Spectral and Polarization Signatures of Shocks in Relativistic Jets

This talk reviews recent progress in our understanding of the multiwavelength spectral and polarization signatures of relativistic shocks in the relativistic jets of active galactic nuclei and gamma-ray bursts. Spectral signatures are based on a self-consistent coupling of Monte-Carlo simulations of diffusive shock acceleration with radiation-transfer simulations. Our results indicate that, in order to reproduce the spectral energy distributions of blazars, the pitch-angle scattering mean free path of electrons has to be strongly energy dependent. Polarization signatures of relativistic shocks are based on polarization-dependent radiation transfer simulations, indicating that large polarization-angle rotations result naturally in a straight jet pervaded by a helical magnetic field. Simultaneous fits to the SEDs, multiwavelength light curves, and time-dependent synchrotron polarization signatures from the prominent polarization-angle swing event in 3C279 are presented.

Speaker: Markus Boettcher (North-West University)

Boettcher_Texas2015.pdf

17:45 Time-dependent Pair Halo Emission from Very-High-Energy Gamma-Ray Sources

Gamma-rays with energy exceeding 100 GeV emitted by extragalactic sources, such as blazars, initiate cascades in the intergalactic medium. The angular and temporal distribution of the cascade photons that arrive at the Earth depend on the strength and configuration of extragalactic magnetic fields (EGMFs) in the line of sight. For weak enough fields, extended emission around the source (halo) is expected to be detectable, and the characteristics (size, energy dependence, and shape) of this emission are a sensitive probe of EGMF strength and correlation length. In this work, we have, for the first time, performed detailed calculations of the time dependence of such blazar halos, in a large range of EGMF parameter space, unconstrained by existing data. I will discuss the quantitative constraints that can be imposed on the EGMF from the recent tentative detection of halo emission around 24 stacked blazars observed with the Fermi LAT, as well as the constraints that can be derived in the absence of such extended emission around GeV and TeV emitting blazars.

Speaker: Foteini Oikonomou

18:10 gap

16:15 → 18:45 03 - Modifications of gravity

Convener: Anne-Christine Davis (Cambridge University)

16:15 Consistent massive graviton on an arbitrary background

The only consistent linear theory for a massive spin-2 field on a flat space-time has been known for a long time as being the Fierz-Pauli theory. Its promotion to a non-linear theory, although essential, has long been thought impossible because of the appearance of the Boulware-Deser (BD) ghost. Recently, de Rham, Gabadadze and Tolley (dRGT) proposed a family of massive gravity theories, free of the BD ghost. In this talk, I will present how to obtain, for the dRGT theories, the linearized equations of motion for a massive graviton. More specifically I will focus on a particular subset of these theories, for which it is possible to remove the need for a second reference metric, hence obtaining the equations of motion of a massive graviton moving in a single and arbitrary background metric. For this specific model I will derive the five covariant constraints necessary to remove five degrees of freedom out of ten, among which the scalar constraint removes the BD ghost. Then I will generalize the covariant constraint analysis to the whole dRGT theories.

Speaker: Laura BERNARD (Université de Paris 6 - Pierre et Marie Curie)

Pres_LB.pdf

16:35 Linear perturbations in massive bigravity: formalism and cosmology

In this talk I will discuss linear perturbations of dRGT massive bi-gravity with a single metric coupled to matter. First, I will introduce the formal derivation of the second order action for generic metrics. I will then use this result to identify stability bounds. Finally, I will discuss the linear perturbations on a FRW background, the cosmology of different branches, the number of degrees of freedom of the theory and the presence of instabilities.

Speaker: Mariele Motta (University of Geneva)

03_1615_Mariele_Linear_Perturbations.pdf

16:55 Gravitational waves in a bigravity model: from inflation to present

In this talk, a detailed analysis of the evolution of tensor perturbations in a cosmological background for a model of Hassan-Rosen theory of bigravity is presented. It is shown that gravitational waves are unstable in this setting, but also that in practice the amplitude of tensor perturbations generated during inflation is sufficiently suppressed to avoid this instability from showing up until today. Hence, this bigravity model cannot be excluded from a pure analysis of the tensor sector. However, stringent limits on inflation from vector and scalar perturbations are derived.

Speaker: Pietro Guarato (Université de Genève)

03_1655_Guarato_Gravitational_waves_in_a_bigravity_model.pdf

17:15 Dualities and Symmetries of Galileons

Galileons appear in the low-energy limit of several cosmologically motivated theories, e.g. Massive Gravity, Bigravity and DGP. Yet we are only just beginning to understand some of their features. I will discuss newly discovered dualities and enhanced symmetries for (subsets of) Galileons and how they are related to scalar-theories of gravity and Massive gravity/Bigravity in particular.

Speaker: Johannes Noller (University of Oxford)

03_1715_Noller_Dualities_and_Simmetries_of_Galileons.pdf

17:35 Quasi-scale invariant inflationary attractors

Recently Kallosh, Linde, and collaborators have provided a unified description of single-field inflation in terms of just one parameter α. These so-called α-attractors predict a spectral index n_s and a tensor-to-scalar ratio r, which are fully compatible with the latest Planck data. The only common feature of all α-attractors is a non-canonical kinetic term with a pole, and a potential analytic around the pole. Starting from the same Einstein frame with a non-canonical scalar kinetic energy, we explore the case of non-analytic potentials and find that they all correspond to quasi-scale invariant gravitational models in the Jordan frame, characterised by a universal relation between r and ns that fits the observational data but is clearly distinct from the one of the α- attractors. Since the breaking of the exact classical scale-invariance in the Jordan frame can be attributed to one-loop corrections, we desume that non-analytic potentials in the non-canonical Einstein frame are physically equivalent to an entire class of models in the Jordan frame, with scale-invariance softly broken by one-loop quantum corrections.

Speaker: Massimiliano Rinaldi (University of Trento)

17:55 Quasi-Static Solutions for Compact Objects in Chameleon Models

It has been suggested that a scalar field φ non-minimally coupled to matter could be responsible for the observed accelerated expansion of the Universe. However, the fact that we are able to measure its effect only on cosmological scales but not on local ones, such as that of our solar system, might be the consequence of a screening mechanism. This is the essence of the Chameleon model. Understanding its viability requires solving the field equations in the transition regime where the scalar field transitions from a region of high density to the outer region where it plays the role of the Dark Energy. In this work we analyze quasi-static spherically symmetric solutions for objects such as standard stars and more compact objects like white dwarfs and neutron stars, by solving the Tolman-Oppenheimer-Volkoff equations coupled with the Klein-Gordon equation in a quasi static regime. We derive a solution that takes into account the background expansion without needing to introduce an artificial cosmic matter corresponding to a non-spatially flat metric. The interior of the star is characterized using a constant density (incompressible) model and a more realistic polytropic equation of state. The increase of compactness that we observe in case of a good screening (thin shell) allows to put serious constraints on the Chameleon mechanism and its viability using astrophysical compact objects.

Speaker: Dr Ilia Musco (Laboratoire Univers et Théories (LUTH) - Observatoire de Paris)

03-1755-Musco-Quasi-Static solutions for compact.pdf

18:15 gap

20:30 → 00:00 Symposium dinner

Thursday 17 December

08:30 → 09:00 Registration

09:00 → 10:45 Plenary talks

09:00 IceCube and the discovery of high-energy cosmic neutrinos

The IceCube project has transformed one cubic kilometer of natural Antarctic ice into a neutrino detector. The instrument detects more than 100,000 neutrinos per year in the GeV to PeV energy range. Among those, we have recently isolated a flux of high-energy cosmic neutrinos. I will discuss the instrument, the analysis of the data, and the significance of the discovery of cosmic neutrinos. The high cosmic neutrino flux observed implies that a significant fraction of the radiation in the non-thermal universe, powered by compact objects from neutron stars to supermassive black holes, is generated by accelerating protons and not just electrons.

Speaker: Prof. Francis Halzen (IceCube/WIPAC)

plenary_0900_Halzen_IceCube.pdf

plenary_0900_Halzen_IceCube.pptx

Video

09:35 The gamma-ray Universe

The last decade has marked a renaissance in the field of gamma-ray astronomy. Results from space and ground-based instruments, in particular Fermi and the big three of ground-based gamma-ray astronomy: HESS, VERITAS and MAGIC, have transformed our view of the gamma-ray sky. The current datasets allow the very detailed study of archetypal particle accelerators across a very wide energy range for the first time, and provide sufficient source counts to constrain population/evolution models for a number of different source classes. The recent results challenge many long-held assumptions in high energy astrophysics and there are also hints of new particle physics. The richness of the results from these instruments provides a strong case for future instrumentation and with the HAWC detector recently completed, and the plans for CTA well advanced, the prospects for highest energy photon astronomy over the next decade are extremely good.

Speaker: Prof. Jim Hinton (Max Planck Institute for Nuclear Physics)

TexasGeneva2015HintonGamma.pdf

Video

10:10 Cosmic ray acceleration and transport

I will summarize the current understanding of the physical processes responsible for cosmic ray acceleration, mainly in supernova remnant shocks, and their transport in the interstellar medium. Special attention will be devoted to the comparison with most recent data of both multifrequency emission from astrophysical sources and spectra of CRs measured locally.

Speaker: Prof. Pasquale Blasi (INAF)

Plenary_1010_Blasi_Cosmic_ray_acceleration.key

Plenary_1010_Blasi_Cosmic_ray_acceleration.pdf

Video

10:45 → 11:20 Coffee break and poster session

11:20 → 12:30 IUPAP young astrophysicist awards

Convener: Prof. Virginia Trimble (UCLA)

11:20 Lest we forget

Astrophysics, both the name and the subject, was born in the halcyon days of irrational international exuberance near the end of the 19th century, when there were 100's of international conferences in a decade and 10's of new international organizations being established. Those included the French-inspired Carte du Ciel and G.E. Hale's International Union for Solar Reseasch. General Relativity; in contrast, came into being in 1915-16, in the darkest days of the Great War that had already put an end to the conferences and would soon abolish most of the organizations. Indeed an August 1914 eclipse expedition from Germany, which Einstein had asked to have a look for bending of statlight by the sun, was imprisoned in the Crimea almost immediately. As the war went on, Karl SchwarIschild, on active duty, worked out his spherically symmetric solution to the Einstein equations, then died of war-related pemphigus. On the astrophysics side, Henry Moseley, who had just put the periodic table into proper order in 1913, died at Gallipoli in July, 1915 (and the Nobel Prize that surely should have been his went to Charles Barkla for 1917). Meanwhile, Paul Merrill learned to sensitize photographic plates for red and IR radiation (to penetrate haze during aerial reconnaissance), which Plates he later used to discover Tc on stellar surfaces, thereby provided incontrovertible evidence that nuclear reactions were occurring in their interiors (plus, of course, convection). A conference among the winning countries held in London in 1918 declared that previously-existing scientific cooperative agreements should be terminated and new societies, involving only those countries "at war with the Central Powers" be formed. And 1919 saw both the founding of the Iliternatienal Astronomical Union and the solar eclipse expeditions, organized by Eddington, which say the bending of star light, at the predicted values which had doubled between Einstein initial 1911 calculation and the definitive GR prediction of 1915-16. Committee No. 1 of the IAU issieg Relativity, under the presidency of Eddington himself1/4 and they voted themselves out of existence (under Levi.-Civita) in 1925 apparently on the grounds that it had all be done. Indeed by then the "expected" gravitational redshifts had'been. reported in spectra of the sun (St. John 1923) and Sirius B (Adams 1 1925)./311th were wrong. High energy astrophysics and cosmology (that is, more or less, applications of SR and GR) did not return to the IAU until 1970 in Brighton UK. Neutral Switzerland and the Netherlands, whose status had been guaranteed under the 1648 Treaty of Westphalia, adhered to the Union only in 1923 (though de Sitter was a VP from 1922) and Germany in 1952, with the Astronomisdhe Gesellschaft initially as the adhering organization for both East and West. R. Gautier and M.G. Bkahuyzen (directors spectively of the Geneva and Leiden Observatories, had attempted to bridge the Great War gap in geodetic observations with the Restricted (meaning neutrals only) Geodetic Association, which then folded into the new Unions by about 1928.

Speaker: Prof. Virginia Trimble (University of California Irvine)

Plenary_1120_Trimble_Lest_we_Forget.pdf

Video

11:40 Award ceremony

Speaker: Prof. Virginia Trimble (University of California Irvine)

plenary_1140_iupap prizesattexas.pdf

plenary_1140_iupap prizesattexas.pptx

11:50 Magnetars: the Universe strongest magnets

Magnetars are a small subset of the neutron star population, being the strongest magnets we know of. They show themselves via powerful X/gamma-ray steady and flaring emission. The energetics of such flares in our Galaxy second only the supernova explosions. In this talk I will first review the observational characteristics of these highly magnetic pulsars, and some recent discoveries in the field. Subsequently, I will present what we currently know about their life-cycle, through detailed simulations of neutron star magneto-thermal evolution and pulsar population synthesis. I will then finish with some considerations on how the study of the Galactic population of magnetars might constrain their possible connection with Gamma Ray Bursts.

Speaker: Nanda Rea (University of Amsterdam/CSIC-IEEC)

plenary_1150_Rea_Magnetars.pdf

plenary_1150_Rea_Magnetars.pptx

Video

12:10 Towards a unified model for the gamma-ray burst prompt emission & a new luminosity-hardness relation for cosmology

The Gamma Ray Bursts (GRBs) are the most intense explosions in the universe and the footprints of stellar-mass black hole formation. Their initial phase, called prompt emission, lasts from a few ms to several tens of s. We suggest here to replace the historical spectral model (Band function) for the GRB prompt emission (keV-MeV energy regime) with a new one. We show that the complex GRB spectro-temporal shapes are well described with a combination of three separate components: (i) a thermal-like component that we interpret as emission from a non-dissipative GRB jet photosphere, (ii) a non-thermal component that we interpret either as synchrotron radiation from charged particles propagating and accelerated within the GRB jet or as a dissipative photosphere, and (iii) a second non-thermal component that is not always present or detectable and which is most likely of inverse Compton origin. The smooth evolution of all three components during the burst duration reinforces the validity of this new model. Detailed studies of the evolution of these components provide insights on the nature and composition of GRB jets as well as on their magnetic fields. Moreover, this new model enables a new luminosity-hardness relation based on the first non-thermal component showing that GRBs may be standard candles. If statistically confirmed, this relation will be used to (i) constrain the mechanisms powering GRB jets, (ii) estimate GRB distances, (iii) probe the early Universe, and (iv) constrain the cosmological parameters in complement to the Type Ia SNe sample. I will present this new model using analysis of GRBs detected with various observatories and instruments such as Fermi, CGRO/BATSE and more recently Swift. I will discuss here the striking similarities of GRB spectral shapes as well as the possible universality of the proposed luminosity-hardness relation in the context of the new model.

Speaker: Sylvain Guiriec (NASA Goddard Space Flight Center / UMD / CRESST)

plenary_1210_Guriec_Towards_Unified_model.pdf

Video

12:30 → 14:00 Lunch break

14:00 → 15:45 05 - Dark matter

Convener: Marco Cirelli (CEA/Saclay)

14:00 Recent Developments on X-ray Signals from Dark Matter Decay in Galaxies and Galaxy Clusters

The latest observational status of the candidate dark matter decay signal at 3.5 keV will be presented. This unidentified X-ray line is observed in multiple galaxies and galaxy clusters. Instrumental effects or plasma emission are disfavoured while the observations are consistent with a decaying dark matter interpretation. In addition to a review of the existing work, the latest developments will be discussed.

Speaker: Jeroen Franse (Leiden University)

Geneva.pdf

14:21 Unveiling the self-coupling of dark matter with galaxy clusters

Recent studies into the dynamics of galaxy clusters and galaxy cluster members have revealed potential signatures of self-interacting dark matter. In this talk I will discuss the current evidence that supports this hypothesis and the observational signals that self-interacting dark matter may manifest itself as. I will finish by presenting current work and observations from the worlds best telescopes that continue to probe this potentially revealing property of the Universe’s most mysterious matter.

Speaker: David Richard Harvey (EPFL - EPF Lausanne)

Texas.key

Texas.pdf

14:42 Multimessenger searches for WIMPs with suppressed interactions

WIMPs with suppressed interactions can present observational challenges at lowest order. We study Majorana DM interacting via an axial-vector Z’, where both the self-annihilation rate and WIMP-nucleon scattering rate are suppressed. By including loop diagrams in the calculation of the self-annihilation rate, we find that the self-annihilation rate is notably enhanced relative to the tree-level rate, and that the branching ratios to gauge-boson final states become non-negligible. We show that the former leads to enhanced constraints on the gamma-ray flux from Fermi and HESS, and the latter leads to stronger constraints on the spin-dependent WIMP-nucleon scattering rate derived from IceCube observations of the neutrino flux from the Sun.

Speaker: Thomas David Jacques (Universite de Geneve (CH))

05_1442_Jacques_Multimessenger searches for wimps with suppressed interactions.key

05_1442_Jacques_Multimessenger_searches_for_wimps_with_suppressed_interactions.pdf

15:03 Non linear evolution of BAO and IR - resummation

Baryon acoustic oscillations (BAO) provide us with one of the most powerful cosmological probes. However, the BAO are plagued by non-linear effects which must be taken into account. I will discuss these effects and their physical impact on correlation functions in real and momentum spaces. I will present a new technique (so-called 'IR — resummation') to account for these effects to all orders in standard Eulerian perturbation theory and time-sliced perturbation theory. I will show that leading and next-to-leading IR — resummation ameliorates remarkably our understanding of two-point and higher-point statistics. Finally, I will touch on the contributions of short-wavelenght perturbations and discuss the possibility of ultraviolet renormalisation.

Speaker: Mikhail Ivanov (Ecole Polytechnique Federale de Lausanne (CH))

Texas_Ivanov.pdf

15:24 Cosmology with the Dark Energy Survey

The Dark Energy Survey (DES) is a 5000 square degree survey targeting dark matter and dark energy science. This year sees the release of the first science results from the DES collaboration using data taken during science verification. I plan to present these new results, which include dark matter maps, cosmology constraints and new discoveries such as the new strong lens systems being found. I will also give an update on the progress of the main science survey.

Speaker: Dr Adam Amara (ETHZ - ETH Zurich)

05_1524_Amara_Dark_Energy_Survey.pdf

14:00 → 15:45 14 - Disks and jets

Convener: Thierry Courvoisier (University of Geneva)

14:00 Narrow-line Seyfert 1 galaxies - rebels of the AGN family

The presence of powerful relativistic jets in narrow-line Seyfert 1 galaxies (NLS1) was confirmed when Fermi detected gamma-rays from a handful of them. In the current active galactic nuclei (AGN) paradigm powerful relativistic jets are produced only in massive elliptical galaxies with supermassive black holes, but NLS1 galaxies challenge this scenario since they have lower black hole masses, higher accretion rates, preferably compact radio morphology and they reside mostly in spiral galaxies. Due to Fermi's discovery the AGN unification schemes have to be revised to fit in NLS1 galaxies. It also invokes questions about the AGN evolution; what triggers and maintains the AGN activity, and what are the evolutionary lines of the different populations? NLS1 galaxies complicate the whole AGN scenario, but also offer a new perspective at the jet phenomena. NLS1 galaxies are a poorly studied class of AGN. It seems that a surprisingly large fraction of them are radio-loud and thus possibly host jets; but also some of them seem to be radio-silent. This, as well as other observational evidence, implies that they do not form a homogeneous class. However, we are not certain what is the origin of the radio loudness, but, for example, the properties of the host galaxy and the large-scale environment might play a role. We used various statistical methods, for example, multifrequency correlations and principal component analysis to study a large sample of NLS1 sources. Here we present the results and discuss the interplay between their properties, such as emission properties, black hole masses, large-scale environments, and their effect on radio loudness. We also present the first results of the Metsähovi Radio Observatory NLS1 galaxy survey and show some highlights of individual sources.

Speaker: Emilia Järvelä (Aalto University Metsähovi Radio Observatory)

ejarvela_texassymposium15.pdf

proc_jarvela.pdf

14:20 Unveiling the parent population of beamed narrow-line Seyfert 1s

Narrow-line Seyfert 1 galaxies (NLS1s) are active galactic nuclei (AGN) recently identified as a new class of $\gamma$-ray sources. The high energy emission is explained with the presence of a relativistic jet observed at small angles, just like in the two classes of blazars. When the latters are observed at larger angles they appear as radio-galaxies, but an analogue parent population for beamed NLS1s has not been determined yet. In this work we analysed this problem by studying the physical properties of three different samples of parent sources candidates: steep-spectrum radio-loud NLS1s, radio-quiet NLS1s and disk-hosted radio-galaxies. In our approach we first derived black hole mass and Eddington ratio from the optical spectra, then we investigated the interaction between the jet and the narrow-line region from the [O III] $\lambda\lambda$ 4959,5007 lines. Finally, the radio luminosity function allowed us to compare their jet luminosity and hence determine the relations between the samples.

Speaker: Marco Berton (University of Padova - Department of Physics and Astronomy "G. Galilei")

14_1420_Berton_Unveiling_the_parent_population.pdf

proc_geneva_v2.pdf

14:40 Broad-band properties of flat-spectrum radio-loud narrow-line Seyfert 1 galaxies

We studied a sample of 42 radio loud narrow-1ine Seyfert 1 galaxies (RLNLS1s) by using all the available multiwavelength observations and the information in literature. The masses of the central black holes are in the range $\sim 10^{6-8}M_{\odot}$, smaller than blazars, while the accretion luminosities span from $\sim 0.01$ to $\sim 0.49L_{{\rm Edd}}$, with an outlier at $0.003$, similarly to quasars. We detected 90% of the sources in X-rays and 17% at $\gamma$ rays. We found hourly variability at high energies. The study of the spectral energy distribution revealed dramatic spectral and flux changes in some sources, suggesting an interplay between the relativistic jet and the accretion disk. The calculated jet power are within the interval $ 10^{42.6-45.6}$ erg s$^{-1}$, generally lower than quasars and BL Lac objects, but partially overlapping with the latter population. Once normalised by the black hole mass, according to the theory by Heinz and Sunyaev (2003), the jet power of the three types of AGN are consistent with each other. This indicates that, despite the observational differences, the central engine of RLNLS1s is quite similar to that of blazars. The historical difficulties in finding radio-loud narrow-line Seyfert 1 galaxies might be due to their low power and to intermittent jet activity. Reference: Foschini et al., 2015, A&A, 575, A13

Speaker: Dr Luigi Foschini (National Institute for Astrophysics - INAF)

Foschini_S14_C51.pdf

Proceedings_Foschini_Talk.pdf

15:00 Quasi-periodic oscillations from relativistic hydrodynamical slender tori

We simulate a purely hydrodynamical torus with constant specific angular momentum around a Schwarzschild black hole. The goal is to search for quasi-periodic oscillations (QPOs) of the torus. Initial torus setup is subjected to radial, vertical and a diagonal (combination of radial and vertical) velocity perturbations. The hydrodynamical simulations are performed using the general relativistic magnetohydrodynamics code Cosmos++ and ray-traced using the GYOTO code. We found that exciting radial perturbations also trigger a plus mode, while vertical perturbations trigger an X-mode. The diagonal perturbation gives just a combination of radial and vertical perturbation. Existing radially perturbed hydrodynamic simulations are in full agreement with our findings. The behavior of QPOs in slender torus mimics those of non-slender torus. This confirms that in actual astrophysical accretion disks, no matter the model (thin, slim, thick), the QPOs will always be detected.

Speakers: Antonis Manousakis, Bhupendra Mishra (Nicolaus Copernicus Astronomical Center Warsaw Poland), Frederic Vincent (Observatoire de Paris)

QPO_Geneva15.pdf

QPO_Poster_TX2015_Geneve.key.zip

15:03 Quasi-Periodic Oscillations are more than just frequencies

Quasi-periodic oscillations (QPO) are an important probe of the timing properties of black-hole binaries and a ubiquitous feature of their PDS. For that reason, many attempts to explain their origin have also reduced them to their frequencies. In order to explore their behavior beyond this, we consider three simple classes of models: elongated hot spots, tori and spirals. We perturb the equilibrium temperature of a thin disk to create these structures. The perturbed disk is supposed to emit blackbody radiation at the local temperature. Radiation is ray-traced in the Schwarzschild metric to a distant observer. We then studied different timing AND spectral features of those models, such as the impact of inclination, how the rms evolves with frequencies, and the impact on the spectral fit; showing how characteristics beyond the frequency could be used to differentiate between models.

Speaker: Frederic Vincent (Observatoire de Paris)

presentation_poster.pdf

proc_QPO_more_than_freq.pdf

15:06 QPOs and Lense-Thirring precession

Observations of QPOs from neutron stars and black holes suggest they must be a feature of the accretion disc surrounding these objects. Their measured frequencies indicate they are from the inner disc, where effects from the Lense-Thirring precession are significant. However, because the properties of the high and low frequency QPOs are so different, it is thought that separate physical processes cause them. We present 3D global simulations of inclined accretion discs and identify features caused by Lense-Thirring precession that may explain both high and low frequency QPOs. We estimate the powerspectra from these simulations and compare these to observations of QPOs.

Speaker: Rebecca Nealon (Monash University)

Sparkler.pptx

Texas_symposium_poster_2015_draft.pdf

15:09 gap

14:00 → 15:45 20 - Future challenges and experiments

Convener: Bruno Leibundgut (European Southern Observatory)

14:00 The Cherenkov Telescope Array

As an observatory for ground-based gamma-ray astronomy in the energy region from a few tens of GeV to a few hundred TeV, the Cherenkov Telescope Array (CTA) will be the major next generation facility of Imaging Atmospheric Cherenkov Telescopes. The broad energy coverage will be accompanied by an order of magnitude improvement in flux sensitivity in the TeV region along with factor 2-5 improvements in angular and energy resolution compared to the current generation of instruments. These improvements in performance will come from the use of multiple designs of wide field-of-view telescope, each optimised for a particular energy region, arranged in extensive arrays. Full sky coverage will come from having arrays at two sites, one in the southern hemisphere and another in the northern. CTA will operate as an open access observatory to the astrophysics community and run a Key Science Programme to provide legacy datasets and address topics of both high-energy astrophysics and fundamental physics. This talk will review the status of the CTA project as it enters its pre-construction phase.

Speaker: Michael Daniel (University of Liverpool)

cta.pdf

CTA_Talk_Texas.pdf

14:24 The e-ASTROGAM mission

e-ASTROGAM is a gamma-ray observatory to be proposed as a Medium-size mission for the ESA science program. It is dedicated to the observation of the Universe with unprecedented sensitivity in the energy range 0.3 – 100 MeV extending up to GeV energies, together with a ground-breaking polarization capability. In this energy window, a variety of phenomena and sources await their discovery and many foundational questions can be answered. The e-ASTROGAM core science is focused on (1) the mysteries of the Galactic centre and inner Galaxy, including the supermassive black hole activity, the Fermi Bubbles, the origin of the Galactic positrons, and dark matter signatures in a new energy window; (2) nucleosynthesis and propagation of heavy elements in our Galaxy and beyond; (3) activity from extreme particle accelerators, including disk-jet transitions in active galactic nuclei and the origin of the extragalactic gamma-ray background. e-ASTROGAM will be uniquely complementary to a variety of ground and space observatories ranging from radio, optical, X-ray and TeV energies, as well as to neutrino and gravitational wave detectors. The e-ASTROGAM payload consists of a single instrument for the simultaneous detection of Compton and pair-producing gamma-ray events. It is based on a very high TRL for all subsystems and includes many innovative features for the main detectors and associated electronics.

Speaker: Vincent Tatischeff (CSNSM, CNRS)

e-ASTROGAM_Texas_Symposium_Dec2016.pdf

14:43 Large Area X-ray Proportional Counter (LAXPC) instrument onboard ASTROSAT

ASTROSAT is India's first science satellite dedicated to multiwavelength astronomy. It has five science payloads which will cover UV to hard X-ray in low earth orbit. LAXPC instrument is one of the major instruments (415 kg payload weight and above 100 electronic cards). This instrument is designed and developed at TIFR and all the three LAXPC flight units have successfully completed all space qualification tests as well as final calibration and have been handed over to ISRO for integration with satellite during 2014. All science payloads have been integrated with satellite in May 2015 and the integrated satellite tests were completed during June-July 2015 and now it is ready to be launched on 28th September, 2015 from Sriharikota, India. We have developed GEANT4 simulations of LAXPC detectors and matched with actual calibration data. In orbit, LAXPC will provide largest effective area in the world for next 5-10 years in 3-80 keV energy range. Large effective area, fine time resolution and moderate energy resolution will allow the LAXPC instrument to probe certain properties of X-ray sources with unprecedented detail. I will describe the salient features of the LAXPC along with calibration results as well as some early results from LAXPC instrument.

Speaker: Prof. J S Yadav (Tata Institute of Fundamental Reaserch)

20_1443_Yadav_Large_Area_X_Ray.pdf

20_1443_Yadav_Large_Area_Xray_proportional_counter.pptx

15:06 XIPE the X-ray Imaging Polarimetry Explorer

XIPE, the X-ray Imaging Polarimetry Explorer, is one of the three missions selected by ESA for study phase for down-selection of the fourth medium size mission. XIPE will measure the polarization in hundreds of celestial sources of different classes. It will allow for answering, in a novel way, to questions related to the acceleration phenomena in PWNe, Supernovae and blazars, to the transport of radiation in plasma embedded in a strong magnetic field like in pulsating X-ray binaries, to the scattering in a-spherical geometries, like in AGNs and in the molecular clouds located in the galactic centre region and, finally, to fundamental physics. It will be operated as a conventional X-ray observatory but providing polarimetry simultaneously to the usual imaging, temporal and spectral information. This is made possible by its unique payload configuration consisting of three Gas Pixel Detector at the focus of three large, albeit low-weight, X-ray telescopes and fitting in the Vega launcher. In this talk I am reviewing the scientific capability of XIPE, the characteristics of the payload and the mission profile.

Speaker: Dr Paolo Soffitta (IAPS/INAF)

SOFFITTA_XPE_TEXAS_2015.pdf

15:25 The X-ray Integral Field Unit for the second large class ESA mission Athena

The Athena mission is the second large mission of ESA with an expected launch date of 2028. The data will be gathered by a very large mirror (2 m2) with a 5 arcsec resolution. Athena will have two instruments: the Wide Field Imager combines a large field of view (40 x 40 arcmin2) with Si-class energy resolution and the X-ray Integral Field Unit (X-IFU) which enables high spectral resolution over a 5’ equivalent diameter field of view. This instrument employs calorimeters which are read-out by Transition Edge Sensors (TES) which operate around ~100 mK. In its baseline configuration, it is made of a monolithic array of 3840 single pixels with a spectral resolution of 2.5 eV. The data will be read-out using Frequency Domain Multiplexing and the cooling system will enable an operational lifetime of more than 5 years. In this paper, we will present the top-level instrument performance and associated science drivers. In addition we will demonstrate the unique capability of this instrument for some relevant science cases. The X-IFU will be provided by an international consortium led by France, The Netherlands and Italy, with ESA member state contributions from Belgium, Finland, Germany, United Kingdom, Poland, Spain, Switzerland together with the United States and Japan.

Speaker: Dr Jan-Willem den Herder (SRON)

20_1525_Herder_X-ray_Integral_Field_Unit_for_Athena.pdf

20_1525_Herder_X-ray_Integral_Field_Unit_for_Athena.pptx

14:00 → 15:45 17 - Activity at the galactic center

Convener: Denys Malyshev (University of Geneva)

14:00 Examining Accretion Disk Properties of Sgr A* Via Stellar Wind Interactions

A recent method has been proposed for probing the properties of the accretion disk surrounding Sgr A* located at our galactic center. This is based on a study of the collision between the disk fluid and the wind of the star, S2. We expand upon the previous work by constructing a semi-analytical model for the shock formation in the stellar wind. This takes into account the thermal pressure of the disk and employs the conservation of momentum flux in the shocked region for deriving the shape of the shock. Our analysis yields semi-analytical expressions for the system as a function of the accretion disk density. For typical values of the latter, we find that the temperature of the shocked stellar wind reaches a few keV. The shocked gas cools via thermal bremsstrahlung emission with a luminosity of $\sim10^{33}erg/s$, assuming solar metallicity. These results have so far been validated by numerical simulations and are within the detection range of current instruments. Ultimately, the detection of these interactions can constrain the density of the disk around the pericenter of the orbit of S2, which will occur in 2018.

Speaker: Mr Ian Christie (Purdue University)

17_1421_Christie_Examining_Accretion_Disk_Properties_of_Sgr_A.pdf

17_1421_Christie_Examining_Accretion_Disk_Properties_of_Sgr_A.pptx

14:21 Reconstruction of the past history of the center of our Galaxy through X-Ray reflection spectra simulations.

In the centre of our Galaxy lies a super-massive black hole, identified with the radio source Sagittarius A*. Sagittarius A* is quite dim in terms of total radiated energy, having a luminosity that is a factor of lower than its Eddington luminosity. However, there is compelling evidence that this source was far brighter in the past. This conclusion was derived from the detection of reflected X-ray emission from the giant molecular clouds in the Galactic centre region. However, the interpretation of the reflected emission spectra cannot be done correctly without detailed modelling of the reflection process. We have developed a Monte Carlo simulation code in order to fully model the complex processes involved in the emerging reflection spectra. The simulated spectra can be compared to real data in order to derive model parameters and constrain the past activity of the black hole. In particular we apply our results to XMM-Newton, Chandra and INTERGRAL observations of Sgr B2, in order to constrain the position and density of the cloud and the incident luminosity of the central source.

Speaker: Mr Michael Walls (DCU)

texas2015-michaelwalls-final.pdf

14:42 Diffuse emissions from radio through microwaves to gamma rays

Diffuse emission has dramatically increased the interest of the astrophysical community, due to recent detailed observations by Planck, Fermi-LAT, H.E.S.S. and VERITAS. Unfortunately disentangling and characterizing this diffuse emission strongly depends on uncertainties in the knowledge of unresolved sources, cosmic rays, matter, radiation fields, and magnetic fields. We discuss here the diffuse emission produced by cosmic rays and its uncertainties. Thanks to observations and comparison of sophisticated models of the diffuse emission from radio through microwaves to gamma rays, we are gaining important insights on CR spectra and intensities throughout the Galaxy and in the inner heliosphere.

Speaker: Elena Orlando (Stanford University)

15:03 NuSTAR Discovery of Galactic Center Hard X-ray Emission

The Galactic Center region contains one of the highest concentration of X-ray sources in the Milky Way. Recently NuSTAR, with its sub-arcminute spatial resolution, has discovered an unresolved hard (20-40 keV) X-ray emission within the central 10 pc. This emission is consistent with either stellar origins, such as large populations of intermediate polars, low-mass X-ray binaries, or millisecond pulsars, or diffuse origins, such as cosmic-ray outows from the supermassive black hole Sagittarius A*. However, each of these explanations implies source properties peculiar to this central region. In particular, the implied average white dwarf mass for the intermediate polar population is $>0.8 M_\odot$. The relation of this population to the much lighter $\sim0.5 M_\odot$ population implied by previous Chandra and XMM-Newton measurements of the surrounding $\sim50$ pc, or to the $\sim0.5$-$0.8M_\odot$ populations implied by previous Galactic bulge and ridge, nearby field, or SDSS survey measurements, is unclear. We present in this contribution details of the central hard X-ray discovery, as well as follow-up work on a possible intermediate polar interpretation. Using the broad-band (3-79 keV) energy resolution of NuSTAR and observations of the intermediate polars TV Columbae and IGR J17303-2601, we argue that both the broad-band NuSTAR measurement of the central 10 pc and the low-energy measurements of the surrounding $\sim50$ pc could be attributed to a single population of intermediate polars with mean white dwarf mass $\sim0.85 M_\odot$.

Speaker: Kerstin Perez

17_1503_Perez_NuSTAR.pdf

15:24 Origin of the gamma-ray emission from the Galactic Centre

The Galactic centre (GC) is a bright gamma-ray source with the GeV-TeV band spectrum composed of two distinct components in the 1-10 GeV and 1-10 TeV energy ranges. The nature of these two components is not clearly understood. We present imaging, spectral, and timing analysis of data from ~7 years of observations of the Galactic centre by FERMI/LAT gamma-ray telescope complemented by sub-MeV data from approximately ten years of INTEGRAL/PICsIT observations. We discuss the implications of our observations for the hadronic and leptonic models of the emission from the GC. We also discuss the spatial morphology of the GC in GeV band and compare our results with the GeV dark matter excess claims.

Speaker: Denys Malyshev (University of Geneva)

17_1524_Malyshev_Origin_of_the_gamma-ray.pdf

14:00 → 15:45 11 - Gravitational waves

Convener: Chiara Caprini (CEA-Saclay)

14:00 Dynamics of compact binaries at the fourth post-Newtonian approximation

Coalescing compact binary systems are among the most promising sources of gravitational waves for the next generations of interferometers. Due to the faintness of the signal, one needs to construct highly accurate templates to be match-filtered against the detector data, for both detection and parameter estimation. During the inspiralling phase of the coalescence, when the two objects are widely separated, the post-Newtonian (PN) formalism allows one to describe the dynamics of the binary and to compute the radiation energy flux, from which the orbital phase evolution can be derived. In this talk, I will present the equations of motion of non-spinnning compact binary systems derived at 4PN in harmonic coordinates. In particular I will detail the formalism based on a Fokker action, including the treatment of the so-called tail effects which appear at 4PN.

Speaker: Ms Laura BERNARD (IAP)

Pres_LB.pdf

14:20 A new instability to black-hole spin precession

We unveil a new dynamical instability in binary black holes with aligned spins. If the spin of the more massive black hole is aligned with the orbital angular momentum while the spin of the less massive black hole is anti-aligned, spins suddenly start to precess when the binary separation falls below the threshold of our newly discovered instability. This instability provides a natural channel to circumvent astrophysical spin alignment at large binary separations allowing significant spin precession prior to merger. The onset of the instability lies in the sensitivity windows of future detectors LIGO/Virgo and eLISA, thus predicting binaries that start precessing while being observed. The instability criterion is derived with novel effective-potential methods to study the black-hole binary dynamics. We double average over both the orbital and the precessional timescale. This allows us to solve the post-Newtonian spin-precession equations analytically for arbitrary mass ratios and spins. These solutions improve our understanding of spin precession in much the same way that the conical sections for Keplerian orbits provide additional insights beyond Newton's 1/r^2 law. More on arXiv:1506.09116 (PRL).

Speaker: Davide Gerosa (University of Cambridge)

texasymptalk.key

texasymptalk.pdf

14:40 Saturation of the f-mode instability in neutron stars

Due to the Chandrasekhar-Friedman-Schutz (CFS) instability, the f-mode (fundamental oscillation) in a newborn neutron star is driven unstable by the emission of gravitational waves. This star is usually the result of a core-collapse supernova explosion, but may also be the aftermath of a binary neutron star merger, where a rapidly rotating, supramassive configuration is formed, before its collapse to a black hole. The instability is halted by non-linear coupling to other modes of the star, which drain energy and saturate it. Depending on the saturation point, the generated gravitational wave signal could be detected by the next generation gravitational wave detectors and, thus, provide useful information about the neutron star equation of state.

Speaker: Pantelis Pnigouras

presentation.pdf

proc_221.pdf

proc_221.zip

15:00 Gravitational wave attenuation through interactions with charged particles

It has been previously shown that the energy lost from an incident gravitational wave (GW) on a cloud of charged particles can manifest itself an electromagnetic field, causing the GW to attenuate. Furthermore, it can be shown that the presence of the field and the circumstances in which it was generated leads to currents and subsequently magnetic fields. We plan to calculate how much energy would be lost by a GW to the cloud of charged particles. We also plan on providing more evidence for the idea that gravitational waves could have created the first magnetic fields in the early universe.

Speakers: Joseph Avenoso (The College of New Jersey), Tyler Viducic (The College of New Jersey)

Geneva_Poster_Final.pdf

15:03 Search of the primordial gravitational waves with Very Long Baseline Interferometry

Some models of the expanding Universe predict that the astrometric proper motion of distant radio sources embedded in space-time are non-zero as radial distance from observer to the source grows. Systematic proper motion effects would produce a predictable quadrupole pattern on the sky that could be detected using Very Long Baseline Interferometry (VLBI) technique. This quadrupole pattern can be interpreted either as an anisotropic Hubble expansion, or as an indication of the primordial gravitational waves in the early Universe. We have analyzed a large set of geodetic VLBI data spanning from 1979 till 2015 to estimate the quadrupole harmonics in the expansion of the vector field of the proper motions of quasars in the sky. We estimated the vector spherical harmonics (three parameters for the dipole and ten - for the quadrupole systematic) by means of analysis of the intermediate individual proper motion. Additionally, the same estimates have been obtained separately for different red shift zones. The results of analysis are presented in this paper.

Speaker: Dr Oleg Titov (Geoscience Australia)

11_1503_Titov_Search_of_the_primordial_GWs_with_VLBI.pdf

proceeding_paper_on_pm.pdf

15:06 gap

14:00 → 15:45 12 - Gravitational lensing

Convener: Ludovic Van Waerbeke (University of British Columbia)

14:00 How the observational quantities of strong gravitational lens effect depend on BH's mass and spin

According to the general relativity (GR), the black hole (BH) is characterized by three parameters: mass $M$, spin angular momentum $J$ and electric charge $Q$. In real cases, the charge is expected to be zero, $Q=0$. Then, the "BH observation" may be understood as the measurement of $M$ and $J$ through a direct observation of GR phenomena, for example the strong gravitational lens effect. I am studying how the two parameters $(M,J)$ appear in a time series data (light curve) seen by single telescope observing the strong gravitational lens effect by Kerr BH. The situation treated in my study consists of three parts as follows: (1) If an emission of light with short duration (burst-like emission) occurs near a BH, we focus on two light rays: One light ray propagates from the source to observer along the shortest path which does not wind around the BH ("direct ray" or "zero-winding ray"). Another ray propagates along the secondary short path which winds once around the BH ("secondary ray" or "1-winding ray"). (2) When the observer detects the 0-winding and 1-winding rays by single telescope, he/she can (in principle) readout following two informations from the light curve seen by the telescope: the time delay $\Delta t_{obs}$ between detection time of 0-winding and 1-winding rays, and the ratio of brightness $R_{obs}$ of 0-winding and 1-winding rays. (3) These two parameters $(\Delta t_{obs} , R_{obs})$ are determined by BH parameters $(M,J)$ and also the position and velocity $(\vec{x},\vec{v})$ of source at the emission. I will report how these quantities $(M,J,\vec{x},\vec{v})$ determine the two observational quantities $(\Delta t_{obs},R_{obs})$. Also, it will be found that the estimated values of $\Delta t_{obs}$ and $R_{obs}$ seem to be detectable by the present telescope capability.

Speaker: Hiromi Saida (Daido University)

SAIDA_Hiromi(2015.Dec.17).pdf

14:21 The future for strong gravitational lensing

The Euclid mission is expected to discover perhaps two orders of magnitude more strong gravitational lenses than are known today. These will be quasar-galaxy, galaxy-galaxy and galaxy-cluster lenses. I will discuss what is required to find and process such a large number of lenses. I will then describe what can be learned from these lenses with respect to the dark matter distribution, cosmology and gravitational theory. In the process I will discuss new methods for analysing lensing data.

Speaker: R. Benton Metcalf (Univerity of Bologna)

12_1421_Metcalf_Strong_Lensing.key

12_1421_Metcalf_Strong_Lensing.pdf

14:42 Search for lensed QSOs in the OGLE survey

We present the results of our search for gravitationally lensed quasars in the OGLE survey. We show candidates from a 650 square degrees area behind the Magellanic Clouds System. The study of strong lensing time delays serves as a powerful probe in cosmology. The OGLE database provides long time light curves, allowing for a cost-effective way to accurately derive time delays and therefore study Hubble constant.

Speaker: Dr Zuzanna Kostrzewa-Rutkowska

ZuzannaKostrzewaRutkowska_OGLElensedQSOs.pdf

15:03 Weak lensing mass map in DECaLS DR1 survey

We present the largest weak lensing mass map covering ~3000 square degrees of the DECaLS DR1 Survey. A good agreement can be found between optical and dark matter maps. Comparing with the mass maps from CFHT Stripe 82 Survey (CS82), the similar high signal-to-noise ratio peaks can be found, which means the systematics of the maps are well controlled. We found ~50,000 WL peaks with SNR higher than 3.0. We also study the cross-correlation between WL peaks and massive clusters and galaxies.

Speaker: Dr Huanyuan Shan (EPFL)

15:24 CMB lensing - galaxy cross-correlations

Large scale structure in the universe causes gravitational lensing of the cosmic microwave background (CMB), which has now been well-measured by several CMB experiments. By cross-correlating CMB lensing with tracers of large scale structure (like galaxies), it is possible to obtain new constraints on cosmology and a better understanding of possible systematic errors in cosmological probes. I will discuss the theoretical formulation, methods used in estimating errors, systematic checks to verify robustness, and cosmological implications of cross-correlations between CMB lensing and galaxy surveys, and will present recent results of cross-correlation analyses.

Speaker: Mr Yuuki Omori (McGill University)

pres3.pdf

14:00 → 15:45 01 - Numerical relativity

Convener: Thomas Baumgarte (Bowdoin College)

14:00 Merger of binary neutron stars: Gravitational waves and mass ejection

The merger of binary neutron stars is one of the most promising gravitational wave sources. For the detection of gravitational waves, numerical relativists are required to accurately predict gravitational waveforms and possible electromagnetic signals. I will talk on our latests effort for the numerical-relativity simulations: magnetohydrodynamics and radiation hydrodynamics simulations.

Speaker: Masaru Shibata (Kyoto University)

texas28.shibata.pdf

texas28.shibata.pptx

14:21 Magnetar formation from the merger of binary neutron stars

I will present results of recent investigations about the possibility to form long-lived or even stable magnetars after the merger of a binary neutron star (BNS) system. BNSs are among the most powerful sources of gravitational waves (GWs) that will be detected by advanced LIGO and Virgo. While the inspiral GW signal is the main target for the first detections, the formation of a long-lived or even stable NS remnant after the merger can produce a long post-merger GW emission that could also be detected. Moreover magnetic fields can be strongly amplified during the merger and this can lead to the formation of a magnetar. Large magnetic fields can have an impact on the GW emission after merger and also lead to electromagnetic counterparts, such as the X-ray plateaus that are observed in short gamma-ray bursts. I will describe the dynamics that can lead to the formation of stable neutron stars after the merger of some BNS systems, how large magnetic fields can be produced, and their possible effects on the GW signal.

Speaker: Bruno Giacomazzo

01_1421_Bruno_Magnetar_Formation.pdf

14:42 Effect of Equation of State on Magnetized Binary Neutron Star Mergers

In this talk I will present some general relativistic magnetohydrodynamic simulations produced with the numerical code WHISKY. We have simulated magnetized binary neutron star mergers with two different Equations of State: ideal-fluid and H4. We have focused in particular on high-mass systems (both equal and unequal-mass ones) that produce after the merger a spinning black hole surrounded by a magnetized accretion disk. These models are indeed one of the main candidates for the central engine of short gamma-ray bursts (SGRBs). I will discuss the possible connection between these models and SGRBs as well as their gravitational wave signal.

Speaker: Mr Takumu Kawamura (University of Trento)

texas_presentation.key

texas_presentation.pdf

15:03 Rotation profile of neutron star merger remnants

A large number of publications model hyper-massive neutron stars (i.e. neutron stars with total mass exceeding the maximum allowed for a uniformly rotating star) produced in binary neutron star mergers by assuming a rotation profile with a rapidly rotating core. We confront such models with results of general relativistic hydrodynamic simulations which exhibit a slowly rotating core instead. Our simulations apply tabulated nuclear physics equations of states including thermal and composition effects, but do not consider neutrino radiation. We investigate the contribution of thermal effects on the structure and short-term stability of the remnant. Further, we discuss if under-densities caused by hot spots contribute to the gravitational wave signal, as well as the influence of the differential rotation on hot spots.

Speaker: Wolfgang Kastaun (Trento University)

remnant_entropy.mp4

remnant_entropy.webm

talk.pdf

15:24 A Hamiltonian approach to relativistic fluid dynamics and binary inspiral

Gravitational waves from neutron-star and black-hole binaries carry valuable information on their physical properties and probe physics inaccessible to the laboratory. Neutron stars can be well-modelled as simple barotropic fluids during the part of binary inspiral most relevant to gravitational wave astronomy, but the crucial geometric and mathematical consequences of this simplification have remained computationally unexploited. In particular, Carter and Lichnerowicz have described barotropic fluid motion via classical variational principles as conformally geodesic. Moreover, Kelvin’s circulation theorem implies that initially irrotational flows remain irrotational. Applied to numerical relativity, these concepts lead to novel Hamiltonian or Hamilton-Jacobi schemes for evolving relativistic fluid flows. Hamiltonian methods can conserve not only flux, but also circulation and symplecticity, and moreover do not require addition of an artificial atmosphere typically required by standard conservative methods. These properties can allow production of high-precision gravitational waveforms at low computational cost.

Speaker: Charalampos Markakis (University of Southampton)

14:00 → 15:45 19 - VHE & CR: CR and astrophysical neutrinos

Convener: Teresa Montaruli

14:00 Correlated neutrino and photon emission during γ-ray flares from the blazar Mrk 421

Blazars, being highly variable sources across the electromagnetic spectrum, may serve as promising targets for high-energy neutrino detection, especially during periods of flaring activity. Using as a testbed the nearby blazar Mrk 421, we present a detailed hadronic model of its emission during a 13-day flare in 2010 with unprecedented multi-wavelength and temporal coverage. We calculate the expected muon neutrino event rate observed by IceCube at energies >1 PeV, and compare it with that expected from a longer, yet non-flaring, period of emission. After applying the derived correlation between the >1 PeV neutrino and 0.1-300 GeV emission to the long-term Fermi/LAT light curve of Mrk 421, we calculate the expected number of muon neutrino events above 1 PeV within 5 years of full IceCube detector livetime and discuss the implications of the results.

Speaker: Dr Maria Petropoulou (Purdue University)

19_1400_Petropoulou_Correlated_neutrino.pdf

Petropoulou_proceeding.pdf

14:25 Diagnose the Sources of IceCube Neutrinos with Fermi Observation

The origin of IceCube detected diffuse neutrinos is still unknown. Searching for their sources also helps to solve the problem of the cosmic ray orgigin. We assume that there is connection between the neutrino and gamma-ray fluxes from the sources. It holds if both the neutrinos and gamma-rays are haronic origin. Moreover, it should also hold in statistic sense even if the gamma-rays are leptonic origin because the ratio of the energy carried by electrons and cosmic rays may be roughly constant. By the neutrino-gamma connection, we use Fermi observations of various candidate sources to constrain the diffuse neutrino origin. We find that the Galactic diffuse neutrino emission contributes less than 10% of the IceCube flux, and point sources cannot account for the IceCube neutrinos either; as for extragalactic candidate sources, neither gamma-ray bursts nor active galactic neuclei jets contribute more than 10%, whereas starburst galaxies may be a promise source for IceCube neutrinos.

Speaker: Zhuo Li (Peking University)

19_1425_Zhuo_li_Diagnose_the_source_of_icecube.pdf

19_1425_Zhuo_li_Diagnose_the_source_of_icecube.ppt

14:45 Searches for ultra-high energy neutrinos and photons with the Pierre Auger Observatory

Ultra-high energy (UHE) neutrinos and photons travel undeflected through cosmic magnetic fields, and point directly to the sources in which they were produced. As such, they have the potential to unveil the locations of the still unknown sources of UHE cosmic rays. The surface detector of the Pierre Auger Observatory is sensitive to UHE neutrinos and photons with energies above 1 EeV and 10 EeV respectively. Inclined air showers (zenith angle $60^{\circ}$ or larger) induced by neutrinos of all flavours (downward- going), and “Earth skimming” tau neutrinos (upward-going) can be identified through the broad time-structure of the signal that is expected to be induced in the detector. UHE photon-induced air showers can be distinguished from hadronic ones on the basis of observables sensitive to the mass composition of the primary particle. In this talk I will present the most recent results from these searches, and discuss the astrophysical implications of these findings for the sources of UHE cosmic rays.

Speaker: Foteini Oikonomou

15:05 Recent results from the ANTARES deep-sea neutrino telescope

The ANTARES experiment has been running in its final configuration since 2008. It is the largest neutrino telescope in the Northern hemisphere. After the discovery of a cosmic neutrino diffuse flux by the IceCube detector, the search for its origin has become a key mission in high-energy astrophysics. Particularly interesting is the indication (although not significant with the present IceCube statistics) of an excess of signal events from the Southern sky region. The ANTARES sensitivity is large enough to constrain the origin of the IceCube excess from regions extended up to 0.2 sr in the Southern sky. Assuming different spectral indexes for the energy spectrum of neutrino emitters, the Southern sky and in particular central regions of our Galaxy are studied searching for point-like objects and for extended regions of emission. The search program also includes multi-messenger analyses requiring time and/or space coincidences with other cosmic probes (cosmic rays, gamma rays or gravitational waves). ANTARES has also provided results on atmospheric neutrinos and searches for rare particles (such as magnetic monopoles and nuclearites in the cosmic radiation). Of particular note are the searches for Dark Matter: the limits obtained for the spin-dependent WIMP-nucleon cross section overcome that of existing direct-detection experiments.

Speaker: Dr Daniele VIVOLO (INFN Napoli)

19_1505_Vivolo_Recent_results_from_ANTARES.pdf

15:25 Exploring the Ultra High Energy Cosmic Rays with the Pierre Auger Observatory

The Pierre Auger Observatory studies the most energetic cosmic rays arriving at Earth, in the energy range from 10^17 eV up to 10^20 eV and beyond. More than 10 years data taking have led to major advances in our knowledge of the origin and nature of cosmic rays. We present a summary of the latest results, discussing the challenges on the astrophysical interpretation of the flux suppression observed above 4 10^19 eV imposed by the experimental results on the primary cosmic ray composition and anisotropy.

Speaker: Sergio Petrera (University of L'Aquila)

Petrera-Auger-Texas-Nobackup.pdf

15:45 → 16:15 Coffee break and poster session

16:15 → 18:45 .

16:15 → 18:45 14 - Disks and jets

Convener: Thierry Courvoisier (University of Geneva)

16:15 Resistive GRMHD simulations of accretion disks around Kerr black holes: connecting large and small scales

Accretion on compact objects is commonly considered the most plausible mechanism to power up a list of astrophysical systems (such as AGNs, GRBs, X-Ray Binaries, etc. . . ) and in particular magnetic fields are believed to play a major role in enabling the accretion process through the development of magnetic instabilities. We investigated the effects of a finite resistivity in a magnetized plasma orbiting around a rotating black hole in a fully covariant framework, providing a self-consistent closure for the Ohm law and performing 3D GRMHD simulations with a highly parallelized version of the ECHO code. We studied in particular the development of the Papaloizou-Pringle instability (PPI) and how it is affected by non-ideal effects, starting with different magnetic configurations and disk models. We also investigate the effects of a mean-field dynamo closure on axisymmetric disks, in order to address the question about the origin of the large-scale magnetic fields required in such systems: starting from a kinematic regime, we extend previous results to take into account a fully dynamical development of the magnetic field through a quenched $\alpha\Omega$-dynamo.

Speaker: Matteo Bugli (Max Planck Institute for Astrophysics)

14_1615_Bugli_Global_simulations_of_magnetized_disks_in_non-ideal_GRMHD.pdf

16:36 Three dimensional global General Relativistic Radiative Magnetohydrodynamical simulations to test stability of thin disk around black hole

The stability of geometrically thin radiation pressure dominated accretion disks around black holes remained under debate. Analytical work concludes that such disks should be thermally unstable. Newtonian shearing box simulations in the past show that these disks may be thermally stable. In last few years other pseudo-Newtonian shearing box simulations showed that the disks are thermally unstable. So basic question arises what is actual fate of the geometrically thin radiation pressure dominated accretion disk ? In order to give better understanding we first time performed three dimensional global General Relativistic Radiative Magnetohydrodynamical (3D GRRMHD) simulations of geometrically thin and radiation pressure dominated accretion disks around black hole. We found that indeed radiation pressure dominated geometrically thin disks are thermally unstable. We treated the disk as optically thick to have strong interaction with radiation.

Speaker: Bhupendra Mishra (Nicolaus Copernicus Astronomical Center Warsaw Poland)

Texax28th_Bhupendra.key

Texax28th_Bhupendra.pdf

16:57 Accretion disk around a super-Eddington accreting neutron star

One of the ultraluminous X-ray sources M82 X-2 was recently identified as a neutron star accreting at a rate significantly larger that ordinary X-ray pulsars. The accretion disc outside the magnetosphere probably still remains below the local Eddington limit but its structure may be affected by the radiation of the central source (accretion column) that together with magnetic torques shifts the centrifugal balance in the inner parts of the accretion disc thus increasing its surface density and thickness. Magnetosphere radius is also affected by the structure of the disc and may be calculated self-consistently in the framework of our model. We consider the structure of such a disc and corrections to the magnetosphere radius. For large magnetic moments (surface magnetic field ~$10^{13}$G), the structure of the accretion disc is very close to the standard accretion disc model (Shakura and Sunyaev, 1973), and magnetosphere radius is proportional to the classical Alfven radius with a constant coefficient. Small magnetic fields, on the other hand, allow the disc to penetrate further inside the magnetosphere, but the radius of the magnetosphere becomes relatively larger with respect to the classic Alfven radius. The inner disc parts in this case show sub-Keplerian rotation (slower by a factor of about 0.75).

Speaker: Anna Chashkina (Tuorla Observatory, University of Turku)

proc.pdf

17:18 Structure of magnetized transonic accretion disks

Using general relativistic analytical treatment in Kerr metric and numerical simulations with the public HARM2D code, we consider the vertical structure and velocity field in the inner parts of a black hole accretion disk, both outside and inside the last stable orbit. Chaotic magnetic fields frozen into the accreting matter easily become the dominant pressure source inside the sonic point that allows to predict the equilibrium thickness of the flow. Numerical simulations, however, reveal instabilities in the magnetic fields leading to formation of current sheets in the super-sonic part of the flow and ultimately to accretion through thin layers (or wisps, in 3D) with the vertical spatial scale much smaller. If disk thickness is large, any consideration of its vertical structure should use some assumptions about the rotation velocity field inside the disk. The latter seems to be strongly dependent upon the presence of a regular magnetic field component near the black hole. If the magnetic flux through the black hole horizon is small, rotation close to the sonic surface conforms very well to Keplerian, and isorotational surfaces have practically cylindrical shapes ($r\sin \theta = const$). We use the assumption of Keplerian cylindrical rotation $\Omega(r,\theta) = \left((r\sin\theta)^{3/2} +a \right)^{-1}$ to estimate the effects of disk thickness upon the Eddington limit and accretion efficiency in black hole accretion disks.

Speaker: Pavel Abolmasov (University of Turku)

B1h-lo.mp4

B1h-mf.mp4

geneva.pdf

proc_abolmasov.pdf

17:38 Thick tori and flows around rotating boson stars

Accretion disks play an important role in the evolution of their relativistic inner compact objects. The emergence of a new generation of interferometers will allow resolving these accretion disks and providing more information about the properties of the central gravitating object. Due to this instrumental leap forward it is crucial to investigate the accretion disk physics near various types of inner compact objects now to deduce later constraints on the central objects from observations. A possible candidate for the inner object is the boson star. Here, we will present the differences between accretion structures surrounding boson stars and black holes. We show that the accretion tori around boson stars have different characteristics than in the vicinity of a black hole. With future instruments it could be possible to use these differences to constrain the nature of compact objects.

Speaker: Zakaria Meliani (LUTH, Observatoire de Paris)

Texas2015_Geneva.pdf

Texas2015_Geneva.pptx

17:59 Transient dynamics of vortices in relativistic regions of accretion disks around black holes.

This work is related to one of the major unsolved problems in the theory of accretion disks: the problem of pure hydrodynamical origin of effective viscosity in their interiors. If it were solved, we would have a general alternative to the well-known conception of supercritical turbulence excited by magneto-rotational instability. As has been widely discussed by fluid physicists since early 1990s, the onset and sustenance of sub-critical turbulence in a spectrally stable shear flow may occur through the so called 'bypass' scenario, when turbulent energy is extracted from the background motion by transiently growing perturbations which are crucially different from modes of perturbations. Homogeneous Keplerian flow, as a model of non-magnetic and non-relativistic thin accretion disk, proved to be the most stable among a variety of differentially rotating flows: it has been shown previously, that transient growth of perturbations, sufficiently large to generate turbulence, can be produced only at Reynolds number beyond 10^6 - 10^7. However, in most of the preceding studies only vortices with length-scales less than the disk thickness have been considered in the context of transient growth phenomenon. Here, we discuss a different type of transiently growing perturbations with azimuthal wavelengths larger than the disk thickness. It turns out, that growth of such perturbations becomes greatly larger as one includes general and special relativistic corrections in Keplerian motion. We suggest that such perturbations, which we refer to as the large-scale vortices, may substantially reduce the critical Reynolds number for the onset of turbulence in relativistic regions of accretion disks around black holes.

Speaker: Viacheslav Zhuravlev

pres.pdf

18:19 Astrophysical Boundary Layers: A New Picture

Accretion is a ubiquitous process in astrophysics. In cases when the magnetic field is not too strong and a disk is formed, accretion can proceed through the mid plane all the way to the surface of the central compact object. Unless that compact object is a black hole, a boundary layer will be formed where the accretion disk touches its surfaces. The boundary layer is both dynamically and observationally significant as up to half of the accretion energy is dissipated there. Using a combination of analytical theory and computer simulations we show that angular momentum transport and accretion in the boundary layer is mediated by waves. This breaks with the standard astrophysical paradigm of an anomalous turbulent viscosity that drives accretion. However, wave-mediated angular momentum transport is a natural consequence of "sonic instability." The sonic instability, which we describe analytically and observe in our simulations, is a close cousin of the Papaloizou-Pringle instability. However, it is very vigorous in the boundary layer due to the immense radial velocity shear present at the equator. Our results are applicable to accreting neutron stars, white dwarfs, protostars, and protoplanets.

Speaker: Mikhail Belyaev (UC Berkeley/TAC)

BL_texas2015.key

BL_texas2015.pdf

18:39 A curved jet model for the synchrotron emission of the BL Lac object PG 1553+113.

We report on the results of a multifrequency campaign on the BL Lac object PG 1553+113 that was organized by the Whole Earth Blazar Telescope (WEBT) Collaboration in 2013 April-August. Nineteen optical, two near-IR, and three radio telescopes monitored the source to follow its behaviour at low energies during and around the high-energy observations by the MAGIC telescopes in April-July. A general bluer-when-brighter trend characterizes the optical emission. We also analyse the UV and X-ray data acquired by the Swift and XMM-Newton satellites in the same period and compare them with previous observations. The long XMM-Newton exposure reveals a curved X-ray spectrum, which shows a harder-when-brighter behaviour on long time scales. In the spectral energy distribution (SED), the XMM-Newton near-UV spectrum is hard, while Swift data display a softer shape that is confirmed by previous HST-COS and IUE observations. An estimate of the synchrotron peak through polynomial fits to the optical-X-ray SED suggests that it lies in the 4-30 eV energy range, with a general increase with X-ray brightness. However, the UV and X-ray spectra do not connect smoothly. We propose an interpretation of the SED shape and variability in terms of orientation changes of the helical structure of an inhomogeneous jet.

Speaker: Dr Antonio Stamerra (INAF-Osservatorio Astrofisico di Torino, Italy)

Stamerra-Raiteri_PG1553_poster.pdf

Stamerra-Raiteri_PG1553_teaser .pdf

18:42 Spectral Analysis of ULXs in Pairs of Interacting Galaxies M51 and NGC 4485/90 Using Swift-XRT

In this study, we report the examinations of the spectra of ULXs in two nearby (< 10 Mpc) pairs of interacting galaxies M51 and NGC 4485/90 collected by Swift-XRT observations from 2005 to 2014 and 2008 to 2015 for each target, respectively. We consider 9 ULXs in M51 and 5 ULXs in NGC 4485/90. We obtain 116 ObsIDs of M51 and 37 ObsIDs of NGC 4485/90. For each pair of interacting galaxy, there are about 10% data that do not meet our criteria for further analysis. The count rate of individual observation ranges from 0.00003 to 0.05 counts/s in 0.3 - 10 keV band with typical errorbar ~ 30%. Some ULXs in M51 exhibit a considerable fluctuation of intensity, up to three times, from 0.01 counts/s to 0.03 counts/s. ULXs in NGC 4485/90 show more stable light curves with no significant changes in intensity. For every source, we divide the data into two categories, e.g. hard-state (those with hardness ratio ≥ 1) and soft-state (those with hardness ratio < 1). Due to the short exposure time during the observation, we got low S/N data with wide errorbar. Therefore, we combine spectrum from many observations with similar spectral characteristics for fitting purpose. We fit the co-added spectra with commonly used models: disk blackbody, power law, and the combination of several models.

Speaker: Ms Lis Sulistiyowati (Institut Teknologi Bandung)

Poster_Spectral_Analysis_ULXs_Swift_XRT.pdf

Presentation_Poster_Spectral_Analysis_ULXs_Swift_XRT.pdf

Proc_Spectral_Analysis_ULXs_Swift_XRT.pdf

16:15 → 18:45 20 - Future challenges and experiments

Convener: Bruno Leibundgut (European Southern Observatory)

16:15 The Galactic Center - a unique laboratory for relativity

Located at 8kpc only, the Galactic Center allows studying a galactic nucleus in unparalleled detail. With the advent of high-resolution, near-infrared instrumentation in the last decade it became possible to follow individual stellar orbits around the radio source Sgr A* with orbital periods as short as 12 years. The orbits determine the mass of Sgr A* to 4 million solar masses, and thus provide compelling evidence for the massive black hole paradigm. Also, variable flare emission originating from the direct vicinity of the event horizon has been discovered. The next generationnear-infrared instrument GRAVITY aims at increasing the resolution further by interferometrrcially combining the light of the four telescopes of the VLT. The resolution achievable is of order 3 milli-arcsec and will allow monitoring stellar orbits with orbital periods of 1 year only. The relativistic prograde periastron precession gets then accessible astrometrically. The astrometric accuracy of GRAVITY is of order of the event horizon size of Sgr A*. This means that we might be able to measure the orbital motion of the flaring emission, and thus that we might have access to measuring the spin of Sgr A*.

Speaker: Stefan Gillessen (Max Planck Inst fur Extraterrestrische Physik)

1615_GC-Genf-2015.pptx

16:35 Space astrometry with Gaia and relativistic astrophysics

Esa's second space astrometry mission Gaia was launched in December 2013 and after an extended commissioning period started its scientific operations in July 2014. After 17 months of observations Gaia delivered an immense dataset of high-accuracy positional observations. In spite of some unexpected difficulties with the instrument, Gaia Data Processing and Analysis Consortium is progressing well towards first data releases scheduled for 2016. This presentation will review the promises and challenges of Gaia space astrometry in the field of relativistic astrophysics. Potential applications of Gaia astrometry in this field range from weak-field tests of general relativity in the gravitational field of solar system to estimates of energy flux for gravitational wave background in a certain frequency domain. Space astrometry can also be used to provide model-independent estimates of the masses of invisible components in some known compact binary systems. The review of these Gaia promises will be accompanied by a critical analysis of the actual performance of the instrument.

Speaker: Prof. Sergei Klioner (Lohrmann Observatorium, Technische Universitaet Dresden)

20_1635_Klioner_space_astrometry.pdf

16:55 Relativistic Astrophysics with ALMA

The Atacama Large Millimetre/Sub-millimetre Array, ALMA, is the leading instrument for observations in the frequency range from 35 to 950 GHz. It is an aperture-synthesis array consisting of 66 antennas of 12 and 7m diameter equipped with sensitive receivers located at 5000m altitude on the Chajnantor Plateau in Northern Chile. ALMA is just entering its third observing cycle and is producing transformational science in many areas of astronomy. I will review ALMA's current and potential contributions to relativistic astrophysics, including the estimation of magnetic fields in accretion disks and the derivation of physical parameters in jets. ALMA is currently being upgraded to act as a phased array, in which the signals from 50 of its antennas are combined to give the equivalent of a single dish with a diameter of 84m. This will allow it to be used as an element of a very sensitive global Very Long Baseline array with a resolution of 10's of microarcsec at 230 and 345 GHz. Imaging of the event horizon shadows around the black holes in the Galactic Centre and M87 will become possible for the first time, leading to stringent tests of General Relativity. The jet launching zone in nearby radio galaxies such as M87 and Centaurus A will be resolved and imaged. Phased ALMA alone will enable complementary tests of General Relativity by finding and timing millisecond pulsars orbiting the Galactic Centre black hole.

Speaker: Robert Laing (ESO)

Laing_ALMA_Texas.pdf

17:15 The Square Kilometre Array Observatory: Prospects for Relativistic Astrophysics

The SKA is now in the detailed design phase with construction scheduled to begin in early 2018, followed by early science from about 2020. A major component of its broad-ranging science program is focused on addressing questions in fundamental physics. The current status of the project will be summarised and the prospects for advancing relativistic astrophysics will be highlighted.

Speaker: Dr Robert Braun (SKA Organisation, Jodrell Bank Observatory)

20_1715_Braun_SKA.pdf

20_1715_Braun_SKA.pptx

17:35 The Large European Array for Pulsars: a leap of the EPTA for gravitational wave detection

Searching for gravitational waves has nowadays been a vital astrophysical experiment in gravity and pulsar timing array (PTA) constitutes the major effort in low frequency regime. The detection of gravitational waves with PTAs relies on the technique of high precision pulsar timing currently achieved with the 100-m class radio telescopes. In this talk, I will present an overview of the Large European Array for Pulsars (LEAP), a key project within the European PTA collaboration to optimally use the largest radio telescopes in Europe to detect gravitational waves. I will first give a brief introduction of the current state-of-the-art EPTA timing observations. I will then provide a description of LEAP's experimental design and an update on its latest status. In addition, I will show the preliminary results on pulsar timing and prospect the contribution of LEAP data into the entire EPTA database, in the light of new limits on gravitational wave background and even the first detection. Finally, I will mention the studies with LEAP on instability of pulsar profiles which will limit the achievable precision of pulsar timing with the next generation of radio telescopes, e.g., the Square-Kilometre-Array.

Speaker: Dr Kuo Liu (Max-Planck-Institute for Radio Astronomy)

LEAP_TEXAS2015.pdf

17:55 The MICROSCOPE mission ready to test the Equivalence Principle in space

MICROSCOPE is a French Space Agency scheduled for launch in 2016, that aims to test the Weak Equivalence Principle in space: one century after the publication of Einstein’s General Relativity, it could allow us to reveal a breach in the theory. Thanks to its cutting-edge-technology inertial sensors, it will allow us to measure the Eotvos parameter down to $10^{-15}$, two orders of magnitude better than the best current constraints. In this talk, I will motivate the science behind MICROSCOPE and present the mission. I will then summarize its status, with an emphasis on how we will tackle the data analysis challenges.

Speaker: Joel Berge (ONERA)

jberge_texas15.pdf

18:15 The High Energy cosmic-Radiation Detection (HERD) Facility onboard China's Future Space Station

The High Energy cosmic-Radiation Detection (HERD) facility is one of several space astronomy payloads onboard China's future Space Station, which is planned for operation starting around 2020. It is designed as a next generation space facility focused on indirect dark matter search, precise cosmic ray spectrum and composition measurements up to the knee energy, and high energy gamma-ray monitoring and survey. HERD is composed of a calorimeter (CALO) surrounded by micro-strip silicon trackers (STKs) from five sides except the bottom. CALO is made of about 10^4 cubes of LYSO crystals, corresponding to 55 radiation lengths and 3 nuclear interaction lengths, respectively. Mont Carlo simulation shows that electrons and photons with a high energy resolution (∼ 1% for electrons and photons and 20% for nuclei) and a large effective geometry factor (> 3 m^2sr for electrons and diffuse photons and > 2 m^2sr for nuclei) can be achieved under this design. Moreover, R&D is under way for reading out the LYSO signals with optical fiber coupled to image intensified CCD and the prototype of 1/40 CALO for beam test at CERN at November this year. Furthermore, the extended design and optimization of HERD for gamma-ray astronomy physics will be discussed in this contribution.

Speaker: Ming Xu (Chinese Academy of Sciences (CN))

HERD_mini_talk.pdf

18:25 Project QVADIS: Testing the existence of the gravitational anomalies by the study of trans-Neptunian binaries

The unrivalled advantage of tiny trans-Neptunian binaries is that they are the best available realisation of an isolated two body system with very weak external and internal Newtonian gravitational field. As a consequence, in many cases (as for instance in the case of the binary (55637) 2002 UX25), the known Newtonian precession of orbit of the satellite is so small that cannot be detected by the existing telescopes; hence an astronomer must observe the zero Newtonian perihelion precession. Fortunately, an observable precession of the orbit can be caused by an anomalous gravitational field as weak as 10-11m/s2 (with the next generation of telescopes the anomalous gravitational field of the order of 10-12m/s might be revealed). In brief, the measurement of a non-zero precession would be sign of new physics, while the measurement of zero-precession would impose strong limits on the size of the eventual gravitational anomalies. The goal of the emerging project QVADIS is to measure the perihelion precession of tiny satellites in some trans-Neptunian binaries. While these measurements are significant independent of any theory they were initially proposed as a crucial test of a new model of the Universe based on the hypothesis that quantum vacuum fluctuations are virtual gravitational dipoles. According to the new model, the only content of the Universe is the known Standard Model matter (i.e. matter made from quarks and leptons interacting through the exchange of gauge bosons) immersed in the quantum vacuum “enriched” with virtual gravitational dipoles. Apparently, what we call dark matter and dark energy, can be explained as the local and global effects of the gravitational polarization of the quantum vacuum by the immersed baryonic matter

Speaker: Dragan Hajdukovic (Institute of Physics, Astrophysics and Cosmology (ME))

QVADIS-Hajdukovic.pdf

QVADIS-Hajduk.proc.pdf

18:35 Testing varying speed of light cosmologies in future experiments.

In this talk I will briefly present the advantages and drawbacks of varying speed of light c cosmologies and relate them to the of varying fine structure constant α theories. Then, I will discuss some new tests (redshift drift and angular diameter distance maximum against Hubble function) which may allow measuring timely and possibly even spatial change of the speed of light. The criteria to detect 1% variability of c by mock data for future missions such as Euclid and SKA (Square Kilometer Array) will be given. Literature: 1. A. Balcerzak, M.P. Dąbrowski, Redshift drift in varying speed of light cosmology, Physics Letters B728, 15-18 (2014). 2. V. Salzano, M.P. Dąbrowski, R. Lazkoz, Measuring the speed of light with Baryon Acoustic Oscillations, Physical Review Letters 114, 101304 (2015). 3. M.P. Dąbrowski, A. Balcerzak, V. Salzano – in progress.

Speaker: Mariusz Dabrowski (University of Szczecin)

1835_Dabrowski_Testing_varying_speed_of_light.pdf

16:15 → 18:45 17 - Activity at the galactic center

Convener: Denys Malyshev (University of Geneva)

16:15 Fermi Bubbles as a probes of Galactic halo environment

Fermi bubbles are giant gamma-ray structures seen above and below the Galactic plane with characteristic size of order of 10 kpc. They also show very good correlation with the microwave emission discovered by the WMAP telescope and the residual diffuse emission in the range above 30 GHz found by the Planck satellite. Correlation between gamma-ray emission observed by Fermi and radio emission observed by Plank implies the presence of high-energy particles in the area covered by Fermi bubbles. These particles may be produced in the Galactic center or accelerated in-situ. Since size of Fermi Bubbles is extremely large, potential transport and acceleration processes are strongly affected by Galactic halo environment and also can affect distribution of Galactic cosmic rays. Thus Fermi Bubbles can be considered as a interesting probe of the magnetic field strength and cosmic ray concentration in the Galactic Halo. We provide a multi-wavelength analysis to set some restrictions on potential models of Fermi bubbles as well as on the propagation of cosmic rays in the central region of our Galaxy.

Speaker: Dmitriy Chernyshov (Lebedev's Institute of Physics, Moscow, Russia)

Chernyshov_Texas-2015_presentation.pdf

16:35 Disrupted globular clusters explain gamma ray excess in the Galactic center

The Fermi satellite has recently detected gamma ray emission from the central regions of our Galaxy. This may be evidence for dark matter particles, a major component of the standard cosmological model, annihilating to produce high-energy photons. We show that the observed signal may instead be generated by millisecond pulsars that formed in dense star clusters in the Galactic halo. Most of these clusters were ultimately disrupted by evaporation and gravitational tides, contributing to a spherical bulge of stars and stellar remnants.

Speaker: Prof. Bence Kocsis (Eötvös University)

17_1635_Kocsis_Disrupted_globular_clusters.pdf

17_1635_Kocsis_Disrupted_globular_clusters.pptx

16:55 Imaging a boson star at Sgr A*

Near-future sub-millimetric VLBI observations of the surroundings of the Galactic center supermassive black hole, Sgr A*, by the Event Horizon Telescope (EHT) will lead to unprecedented constraints on the nature of the accretion flow surrounding this compact object. One of the most fascinating goal of the EHT is to test the presence of an event horizon by imaging the *black hole shadow*, and to constrain the Kerr metric by measuring the so-called *photon ring*. The goal of my talk will be to present the first simulations of an accretion flow at Sgr A* assuming that this compact object is no longer a black hole, but a boson star. Such an object is a long-studied alternative to black holes, which does not possess any event horizon, nor any singularity. I will show images and spectra of an accretion torus surrounding a boson star at Sgr A*, and discuss the specific observational properties of rotating boson stars as opposed to Kerr black holes. I will focus in particular on the (im)possibility to demonstrate the existence of an event horizon from detecting Sgr A* shadow.

Speaker: Dr Frederic Vincent (Observatoire de Paris)

BS.pdf

17:15 The Radio Evolution of the Galactic Center Magnetar

While the radio emission of magnetars is notable for its peculiar spectrum and significant variability, the behavior of the Galactic Center magnetar is odd for even this class of neutron stars. In this talk, I will present the broadband spectrum and high frequency (44 GHz) properties of this magnetar in early to mid 2014, when the source transitioned from a fairly constant radio flux and pulse profile to significant variability in both. These results provide important information regarding the physical processes responsible for this transformation.

Speaker: Joseph D Gelfand

gc_magnetar.pdf

gc_magnetar.pptx

17:35 Proposed Laboratory Simulation of Galactic Positron In-Flight Annihilation in Atomic Hydrogen

Positron annihilation at 511 keV coming from the direction of the Galactic Center could be occurring in a variety of different ways. One channel, in-flignt annihilation, occurs by charge exchange approximately below 100 eV as positrons slow by inelastic collisions from keV energies. The characteristic Doppler broadened line width and shape is of interest in comparing to galactic gamma ray data from the SPI/Integral telescope.[1] Laboratory experiments in the 1980's simulated annihilation in-flignt in molecular hydrogen and helium.[2] However, the laboratory simulation in atomic hydrogen, proposed here, has only been done with Monte Carlo methods to date. There is a discrepancy of a factor of two in the present laboratory measurements of the positron-atomic hydrogen impact ionization cross section, which affects the predicted in-flight annihilation line-width appreciably. Thus, laboratory measurements of in-flight positron annihilation in atomic hydrogen will be useful at this time to accurately predict this possible component of the Doppler broadened 511 keV annihilation radiation from the Galactic Center. [1.] E. Churazov, S. Sazonov, S. Tsygankov, R. Sunyaev, D. Varshalovich, 2010, Mon. Not. R. Astron. Soc. 411, 1727. [2.] B. L. Brown, M. Leventhal, A.P. Mills, & D.A. Gidley, 1984, Phys. Rev. Lett. 53, 2347.

Speaker: Prof. Benjamin Brown (Marquette University)

17_1715_Brown_Proposed_laboratory_simulation_of_galactic.pdf

17_1715_Brown_Proposed_laboratory_simulation_of_galactic.pptx

17:55 gap

16:15 → 18:45 11 - Gravitational waves: Pulsar Timing Array

Conveners: Michael Kramer (Max-Planck-Institut fuer Radioastronomie), Victoria Kaspi

16:15 Gravitational waves from binary supermassive black holes missing in pulsar observations

Gravitational waves are expected to be radiated by supermassive black hole binaries formed during galaxy mergers. A stochastic superposition of gravitational waves from all such binary systems will modulate the arrival times of pulses from radio pulsars. Using observations of millisecond pulsars obtained with the Parkes radio telescope, we constrain the characteristic amplitude of this background, $A_{\rm c,yr}$, to be < $1.0\times10^{-15}$ with 95% confidence. This limit excludes predicted ranges for $A_{\rm c,yr}$ from current models with 91-99.7% probability. We conclude that binary evolution is either stalled or dramatically accelerated by galactic-center environments, and that higher-cadence and shorter-wavelength observations would result in an increased sensitivity to gravitational waves.

Speaker: Dr Stefan Oslowski (Bielefeld University / MPIfR Bonn)

Oslowski_Texas2015.pdf

16:36 Status of the European Pulsar Timing Array

The European Pulsar Timing Array is a collaboration between European research institutes and radio observatories that was established in 2006. The EPTA makes use of the five largest radio telescopes at decimetric wavelengths in Europe: the Effelsberg Radio Telescope, the Lovell Radio Telescope, the Nançay Radio Telescope, the Westerbork Synthesis Radio Telescope and the Sardinia Radio Telescope. The main goal of the EPTA is the direct detection of gravitational waves using high-precision timing of an ensemble of millisecond pulsars. We will present here the status of the EPTA and show some of the latest pulsar timing results obtained with nearly 20 years of data.

Speaker: Gregory Desvignes

talk.pdf

16:57 Search for continuous gravitational wave in EPTA dataset

We have searched for continuous gravitational wave (CGW) signals produced by individually resolvable, circular supermassive black hole binaries (SMBHBs) in the latest EPTA dataset, which consists of ultra-precise timing data on 41 millisecond pulsars. Several algorithms have been used and depending on the adopted detection algorithm, the 95% upper limit on the sky-averaged strain amplitude lies in the range 6 x 10^-15 < A < 1.5 x 10^-14 at 5 nHz < f < 7 nHz. The most robust upper limit – obtained via a full Bayesian analysis searching simultaneously over the signal and pulsar noise on the subset of our six best pulsars – is A ~10^-14. These limits, the most stringent to date at f < 10 nHz, exclude the presence of sub-centiparsec binaries with chirp mass Mc > 10^9 solar masses out to a distance of about 25 Mpc, and with Mc > 10^10 solar masses out to a distance of about 1 Gpc (z~ 0.2).

Speaker: Dr Antoine Lassus (Max Planck Institute für Radioastronomie)

17:19 Limits on the amplitude of the nanohertz gravitational wave Universe from the European Pulsar Timing Array

The European Pulsar Timing Array (EPTA) was established in 2006 as a collaboration between European research institutes and radio observatories. The key mission of the EPTA is the direct detection of nanohertz gravitational waves (GWs) using the high-precision timing of an ensemble of millisecond pulsars. The primary source of GWs in the nanohertz band is expected to be merging supermassive black hole binaries (SMBHBs). We will present recent results from the EPTA that set limits on the amplitude of an isotropic, or anisotropic gravitational wave background, formed from the super position of signals from a large population of these SMBHBs, as well as limits on the amplitude of GWs from individual sources. Finally we will discuss recently introduced methods of improving the sensitivity of timing arrays to GWs by performing the analysis using profile data.

Speaker: Dr Lindley Lentati (Cambridge University)

EPTALimits.key

EPTALimits.pdf

17:41 Lessons on massive black hole binaries from pulsar timing arrays

Pulsar timing arrays (PTAs) are dramatically improving their sensitivity. Current upper limits start to be in tension with vanilla models of gravitational wave driven, circular supermassive black hole binaries (SMBHBs), although nothing can be safely ruled out yet. I will discuss how we can use current and future PTA limits to investigate the nature of SMBHBs and learn about their overall cosmic population and the dynamics bringing them to the final gravitational wave driven merger.

Speaker: Dr Alberto Sesana (University of Birmingham)

11_1741_Sesana_Pulsar_timing.pdf

18:03 Constraining the energy scale of cosmic strings with PTAs

Pulsar Timing Arrays observe a set of millisecond pulsars at high timing precision over long periods of time, aiming to directly detect gravitational waves. Probing the nHz frequency regime, PTAs are sensitive also to many primordial GW sources, with one of them being cosmic strings; a web of string-like energy concentrations that may have formed right after Inflation and permeates the Universe. In this talk, I will give a brief introduction to these exotic sources, describe why they are so interesting from a cosmological perspective, and show that PTAs is the best tool currently available for the detection of their GW signatures. Since current PTA projects have only managed to set upper limits on the amplitude of a potential SGWB, I will show how these limits can be translated to limits of the energy scale, or tension in other words, of cosmic strings. In particular, I will present the latest upper limits on the string tension by the EPTA and NANOGrav. The generic way in which these limits have been computed, grant them robustness close to those computed by CMB data, and for the first time, such PTA results have reached and surpassed, the best available CMB-originating tension limits from Planck.

Speaker: Dr Sotiris Sanidas (University of Amsterdam)

sanidas_texas2015.pdf

18:25 Pulsar timing detection of gravitational waves from supermassive black hole binaries in stellar environment

We study the effect of stellar environment on gravitational wave spectrum produced by supermassive black hole binaries (SBHB). Our model includes the possibility of rotating galactic nucleus, which opens a new degree of freedom - the orientation of SBHB’s orbital plane - and significantly affects its eccentricity evolution. The result of our work is a model spectrum of stochastic gravitational wave background which can be tested by pulsar timing array observations.

Speaker: Alexander Rasskazov

texas 2015.key.pdf

texas 2015.key.zip

16:15 → 18:45 12 - Gravitational lensing

Convener: Ludovic Van Waerbeke (University of British Columbia)

16:15 Where are the baryons?

In the local Universe, about half of the total baryon content of the Universe is still escaping our census. Understanding the state and distribution of these missing baryons is a major question for our knowledge of galaxy evolution and cosmology. Numerical simulations predict that the missing baryons should be in the form of a very diffuse, warm-hot (T~1e5-1e7 K) state, which would remain largely undetected both inside dark-matter halos and in the filaments of the cosmic web. I will present recent results on the hunt for the missing baryons. First, I will present a combined X-ray and gravitational lensing study of filaments in the outskirts of a massive galaxy cluster, which unveil the baryon content of intergalactic filaments. I will also show the results of systematic studies of the global baryon budget of massive halos in the XXL and CFHTLS surveys. These measurements will be combined to update our knowledge of the Universe's missing baryons.

Speaker: Dr Dominique Eckert (University of Geneva)

eckert_texas2015.pdf

16:35 A direct measurement of tomographic lensing power spectra from CFHTLenS

We measure the weak gravitational lensing shear power spectra and their cross-power in two photometric redshift bins from the Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS). The measurements are performed directly in multipole space in terms of adjustable band powers. For the extraction of the band powers from the data we have implemented and extended a quadratic estimator, a maximum likelihood method that allows us to readily take into account irregular survey geometries, masks, and varying sampling densities. We find the 68 per cent credible intervals in the $\sigma_8$--$\Omega_{\rm m}$-plane to be marginally consistent with results from $Planck$ for a simple five parameter $\Lambda$CDM model. For the projected parameter $S_8 \equiv \sigma_8(\Omega_{\rm m}/0.3)^{0.5}$ we obtain a best-fitting value of $S_8 = 0.768_{-0.039}^{+0.045}$. This constraint is consistent with results from other CFHTLenS studies as well as the Dark Energy Survey. Our most conservative model, including modifications to the power spectrum due to baryon feedback and marginalization over photometric redshift errors, yields an upper limit on the total mass of three degenerate massive neutrinos of $\Sigma m_\nu < 4.53 \, {\rm eV}$ at 95 per cent credibility, while a Bayesian model comparison does not favour any model extension beyond a simple five parameter $\Lambda$CDM model. Combining the shear likelihood with $Planck$ breaks the $\sigma_8$--$\Omega_{\rm m}$-degeneracy and yields $\sigma_8=0.817_{-0.014}^{+0.013}$ and $\Omega_{\rm m} = 0.298 \pm 0.011$ which is fully consistent with results from $Planck$ alone.

Speaker: Fabian Köhlinger

12_1635_Koehlinger.pdf

16:55 Gravitational microlensing as a probe for dark matter

We study effects due to a possible presence of putative dark matter mini-halos (DM clumps) in the light curves of source images of the extragalactic gravitational lens systems. The extended clumps are described by means of a simplified model of the lens mapping. Every microlens consists of a central point mass surrounded by a concentric extended mini-halo; this is characterized by the ratio q of the extended mass to the point one, the typical size R and the total mass M. We consider the microlensing of a remote source by a stochastic system of such microlenses. The spatial distribution of microlenses is assumed to be uniform; the distribution of M have been chosen according to the Salpeter law for different fixed values of R and q. To have a significant effect we have chosen the size R to be comparable with the radius of the Einstein-Chwolson ring of a microlens. The motion of a source with respect to the microlenses induces a dependence of the amplification of the source image upon the time (amplification curve). We obtain an ensemble of the amplification curves for a number of realizations of the microlensing field. This is used to derive autocorrelation functions of the light curves by means of an averaging procedure. The derivation is fulfilled for different values of the microlensing optical depth and the external shear, as well as for different values of q and R.

Speaker: Vitalii Sliusar (Astronomical Observatory of Taras Shevchenko National University of Kyiv, Ukraine)

Sliusar_Zhdanov_Alexandrov-Microlensing_as_a_probe_for_dark_matter.pdf

17:15 Test of relativistic gravity using the microlensing of broad iron line in quasars

We show that observation of the time-dependent effect of microlensing of relativistically broadened emission lines (such as e.g. the Fe Kalpha line in X-rays) in strongly lensed quasars could provide data on celestial mechanics of circular orbits in the direct vicinity of the horizon of supermassive black holes. This information can be extracted from the observation of evolution of red / blue edge of the magnified line just before and just after the period of crossing of the innermost stable circular orbit by the microlensing caustic. The functional form of this evolution is insensitive to numerous astrophysical parameters of the accreting black hole and of the microlensing caustics network system (as opposed to the evolution the full line spectrum). Measurement of the temporal evolution of the red / blue edge could provide a precision measurement of the radial dependence of the gravitational redshift and of velocity of the circular orbits, down to the innermost stable circular orbit. These measurements could be used to discriminate between the General Relativity and alternative models of the relativistic gravity in which the dynamics of photons and massive bodies orbiting the gravitating centre is different from that of the geodesics in the Schwarzschild or Kerr space-times.

Speaker: Ievgen Vovk

GR_test.pdf

GR test.ppt

17:35 Gravitational lensing flexion measurements in the Hubble Frontier Fields

Flexion is the second order weak gravitational lensing effect which is responsible for the arclike appearance of lensed sources. Its strong signal in the intermediate regime and the orthogonality to the weak lensing shear field make flexion an ideal complement to today's gravitational lensing measurements. Furthermore, its high sensitivity to local density peaks makes it a great tool for detecting substructure and thus for constraining the halo mass function. This could potentially distinguish cold and warm dark matter scenarios. However, flexion measurements have proved to be difficult up to now. The high quality of the *Hubble Frontier Fields*, a major observing program with the *Hubble Space Telescope* to provide unprecedented deep observations of 6 strong lensing clusters, makes this data set a prime target for flexion measurements. We present an automated measurement pipeline and substructure constraints from its application to the clusters MACSJ0416.1-2403 and Abell 2744.

Speaker: Mr Markus Rexroth (EPFL - EPF Lausanne)

Poster.pdf

17:38 Effects of the second-order vector mode on weak lensing signals

Vector mode of cosmological perturbation theory imprints characteristic signals on the weak lensing signals such as curl- and B-modes which are never imprinted by the scalar mode. However, the vector mode is neglected in the standard first-order cosmological perturbation theory since it only has a decaying mode. This situation changes if the cosmological perturbation theory is expanded up to second order. The second-order vector and tensor modes are inevitably induced by the product of the first-order scalar modes. We study the effect of the second-order vector mode on the weak lensing curl- and B-modes. We find that the curl-mode induced by the second-order vector mode is comparable to that induced by the primordial gravitational waves with the tensor-to-scalar ratio $r = 0.1$ at $\ell \approx 200$. In this case, the curl-mode induced by the second-order vector mode dominates at $\ell > 200$. Furthermore, the B-mode cosmic shear induced by the second-order vector mode dominates on almost all scales. However, we find that the observational signatures of the second-order vector and tensor modes cannot exceed the expected noise of ongoing and upcoming weak lensing measurements. We conclude that the curl- and B-modes induced by the second-order vector and tensor modes are unlikely to be detected in future experiments.

Speaker: Mr Shohei Saga (Naogya university)

poster_talk.pdf

17:41 Black Holes, Neutron Stars and White Dwarf Candidates from Microlensing with OGLE-III

Most stellar remnants so far have been found in binary systems where they interact with matter from their companion. Isolated neutron stars and black holes are hard to find as they do not emit light, yet they are predicted to be present in our Galaxy in vast numbers. We explored the OGLE-III database of 150 million objects observed in years 2001-2009 and found 59 microlensing events exhibiting parallax effect due to Earth’s motion around the Sun. Combining parallax and brightness measurements from microlensing light curves with expected proper motions in the Milky Way, we identify 15 microlensing events which are consistent with having a white dwarf, neutron star or a black hole lens and we estimate their masses and distances. The distribution of masses of our candidates indicates a continuum in mass distribution with no mass gap. We also present predictions on how such events will be observed by the astrometric Gaia mission.

Speaker: Dr Zuzanna Kostrzewa-Rutkowska (Warsaw University Astronomical Observatory)

posterGeneva2015-MicrolensingBHs.pdf

17:44 How to use geodetic VLBI to measure relativistic light deflection from extragalactic objects

The Sun's gravitational field deflects the apparent positions of close objects in accordance with the formulae of general relativity. Optical astrometry is used to test the prediction, but only with the stars close to the Sun and only during total Solar eclipses. Nowadays, more advanced technique, geodetic Very Long Baseline Interferometry (VLBI) is applied for testing of general relativity with precision about 0.01 percent. The geodetic VLBI is capable of measuring the gravitational delay based on the differential Shapiro's delay. By reason, the gravitational delay is equivalent to the deflection of the light from distant radio sources and could be measured at anytime and across the whole sky. In accordance with the theory, all celestial objects display annual circular motion with the magnitude proportional to their ecliptic latitude due to the Earth orbital motion. In particular, the objects near the ecliptic pole draw an annual circle with magnitude of 4 millisecond of arc. In contrast to the optical facilities, a single ground-based VLBI interferometer is made of two radio telescopes separated by several thousand kilometers. This provides an additional advantage to detect a secondary light deflection angle caused by the parallactic shift of the Sun as observed from both ends of the interferometer. This effect is proportional to the baseline length and is about 0".01 for grazing light at baseline of 8000 km. It could be used in future space interplanetary VLBI missions with baseline length of one billion kilometers (comparable to the Jupiter orbit size) for direct detection of invisible mass from extragalactic objects.

Speaker: Oleg Titov

12_1804_Titov_How_to_use_geodetic_VLBI_to_measure_relativistic_light_deflection.pdf

17:47 gap

16:15 → 18:45 01 - Numerical relativity

Convener: Thomas Baumgarte (Bowdoin College)

16:15 CAFE: A relativistic Magnetohydrodynamics code

We present CAFE, a code designed to solve the equations of relativistic ideal magnetohydrodynamics (RMHD) in three cartesian dimensions. We present the standard tests for the relativistic RMHD regime. The tests include among the two-dimensional (2D) and 3D tests with magnetic field. The code uses high-resolution shock-capturing methods, and we present the error analysis for a combination that uses the Harten, Lax, van Leer, and Einfeldt flux formula combined with a linear, PPM and WENO5 reconstructors. We use the flux-constrained transport and the divergence cleaning methods to control the divergence-free magnetic field constraint.

Speaker: Alejandro Cruz Osorio (Universidad Nacional Autónoma de México)

01-1615-Osorio-CAFE- a relativistic.key

01-1615-Osorio-CAFE-_a_relativistic.pdf

16:35 Simulating the start of inflation from inhomogeneous initial conditions

A period of exponential expansion early in our cosmic history is usually invoked to explain the large scale homogeneity and isotropy of the Universe. However, there remain important questions about the conditions under which inflation can actually start when homogeneity is not assumed to begin with it. In this talk, I will present results from fully general-relativistic simulations used to understand the circumstances under which a period of exponential expansion can eventually arise from initial conditions where the gradient and kinetic energy of the putative inflaton dominates over the potential energy. This allows us to study what happens in a number of different cases, both when using different inflaton potentials, as well as when considering a range of different scales for the inhomogeneities. In particular, we study the regime where the length scale of the inhomogeneities is comparable to the average Hubble radius, and where the gravitational pull of the over-densities is strong enough to form black holes.

Speaker: Dr William East (Stanford University)

east.pdf

16:55 Critical Collapse of Radiation Fluids: Deviations from Spherical Symmetry

We study critical phenomena in the gravitational collapse of a radiation fluid. We perform numerical simulations in both spherical symmetry and axisymmetry, and observe critical scaling in both supercritical evolutions, which lead to the formation of a black hole, and subcritical evolutions, in which case the fluid disperses to infinity and leaves behind flat space. We identify the critical solution in spherically symmetric collapse, and study the approach to this critical solution in the absence of spherical symmetry. Our simulations are performed with an unconstrained evolution code, implemented in spherical polar coordinates, and adopting ``moving-puncture" coordinates.

Speaker: Thomas Baumgarte (Bowdoin College)

01_1655_Baumgarte_critical_collapse_of_radiation_fluid.pdf

17:15 Evolution of a self-gravitating spherical massless scalar field on compactified constant mean curvature hypersurfaces

I present the numerical evolution of a self-gravitating massless spherical scalar field based on a new code which implements the 3+1 tetrad formulation of general relativity on compactified constant mean curvature (CMC) hypersurfaces developed by Bardeen, Sarbach and Buchman. The major advantage of this formulation is that it allow us to model with high accuracy the scalar radiation at future null infinity, removing the need to impose artificial outer boundary conditions. As a test case of study, I explore the evolution of different initially in-going packets or shells of scalar fields and compare the results to standard results in the literature, including Choptuik's results on critical collapse.

Speaker: Manuel David Morales (Instituto de Física y Matemáticas - Universidad Michoacana de San Nicolás de Hidalgo)

01-1715-Morales-Evolution of a self-gravitating.pdf

17:35 Black hole mimickers

We show that a spherically symmetric gravitational collapse of a star can result in a bounce if the equation of state behaves with sufficient rigidity just before the formation of an event horizon. The relativistic time dilation produced by the strong gravity makes the whole process to be undistinguishable from a black hole on timescales shorter than the Hubble time for a distant observer. We solve the Misner-Sharp equations for stellar collapse with a suitable equation of state that reduces to a polytropic at low densities and mimicks an effective cosmological constant during the collapse, finally inverting the direction of the velocity field of the fluid. We also present some preliminary results of numerical simulations of these objects. We conclude that evolving gravitational systems might mimick, in this way, most of the properties attributed to static black holes.

Speaker: Mrs Daniela Perez (Instituto Argentino de Radioastronomia)

conf_fact_1.ps

fig1.eps

Perez-et-al-Pro-Texas.pdf

Perez-et-al-Pro-Texas.tex

rho_1.ps

Texas_DanielaPerez-final.pdf

Texas_DanielaPerez-final.ppt

17:55 The nature of trapping horizons in collapses forming black holes

In the context of gravitational collapse to form a black hole, one sees the appearance of inner and outer trapping horizons (foliated by marginally trapped surfaces), as was already noted in numerical calculations in the 1960s. This phenomenology has acquired new interest in connection with discussions of the Hayward unified first law of black hole dynamics. We have investigated the nature of the inner and outer horizons (ie whether they are spacelike, timelike or null), making contact with the Misner-Sharp formalism used in calculations for collapse of spherically symmetric fluid configurations to form black holes. By means of numerical simulations, we have followed the R=2M condition dynamically during the gravitational collapse, and have found that the nature of these trapping horizons is given by a very simple expression depending on the equation of state, related also to the velocity of the horizon with respect the collapsing fluid. Whether these horizons are spacelike or timelike plays an important role in in classical depletion and quantum evaporation of black holes because only timelike or null horizons allow particles to pass through. We have observed different behaviours for the cases of stellar collapse and primordial black hole formation within an expanding Universe, resulting from the different nature of the matter involved. In this talk we will present results from our investigations.

Speaker: Dr Ilia Musco (Laboratoire Univers et Théories (LUTH) - Observatoire de Paris)

01-1755-Musco-The nature of trapping horizons.pdf

18:15 Asymptotic evolution of Robinson-Trautman spacetimes

By exploring the numerical scheme introduce in [1], we analyze the asymptotic ($u\to\infty$) evolution of Robinson-Trautman spacetimes, with special emphasis on the behavior of the apparent horizon and its curvature anisotropies, which can indeed induce accelerations and a recoil in the remnant black hole due to asymmetrical emission of gravitational waves [2]. **References** [1] A. Saa and R.P. Macedo, *Gravitational wave recoil in Robinson-Trautman spacetimes*, Phys. Rev. **D78**, 104025 (2008) [arXiv:0809.3039]. [2] L. Rezzolla, R.P. Macedo, J.L. Jaramillo, *Understanding the "anti-kick" in the merger of binary black holes*, Phys. Rev. Lett. **104**, 221101 (2010) [arXiv:1003.0873].

Speaker: Alberto Saa (UNICAMP)

18:18 break

16:15 → 18:45 19 - VHE & CR: CR and astrophysical neutrinos

Convener: Matthieu Heller (Universite de Geneve (CH))

16:15 Study of the galactic cosmic ray energy spectrum with the ARGO-YBJ experiment

The CR spectrum has been studied by the ARGO-YBJ experiment in a wide energy range (TeVs→ PeVs) . This study is particularly interesting because not only it allows a better understanding of the so called ’knee’ of the energy spectrum and of its origin, but also provides a powerful cross-check among very different experimental techniques. The unique detector features (full coverage, time resolution, large dynamic range) and location (4300 m above sea level) allowed both lowering the energy threshold down to the region covered by direct measurements and reaching the knee of the all-particle spectrum, where data from many ground-based experiments are available since long time. Moreover, the possibility of a detailed study of the particle distribution at ground in the first few meters from the shower axis, provided a new and efficient way of selecting events initiated from light mass primaries (i.e. protons and alpha particles), without relying on the muon signal, thus avoiding sizeable systematic dependencies on the adopted hadronic interaction model. The resulting all-particle spectrum (measured in the energy range 100 TeV - 10 PeV) is in good agreement with both theoretical parametrizations and previous measurements, thus validating the selection and reconstruction procedures. The light-component (i.e. p + He) has been measured from 3 TeV up to about 3 PeV. The ARGO-YBJ result, while being in agreement with highest energy direct measurements, shows a clear indication of a bending below 1 PeV. This provides new important inputs to acceleration/propagation models for galactic cosmic rays.

Speaker: Antonio Surdo (INFN - Lecce (IT))

ARGO_Gal_CRspectrum.pdf

ARGO_Gal_CRspectrum.pptx

Argo_GalCRspectrum_proc.pdf

16:35 The universal model of cosmic ray production

It seems to be a striking coincidence that all putative cosmic ray sources which are dynamically able to fill the universe with the observed extragalactic cosmic ray density can produce the same maximum confinement energy, eBR ~ 10^20 eV, while being spread in scale R over 10 orders of magnitude - the most impressive representation of this coincidence is the famous Hillas plot, in which all "interesting" sources of extragalactic cosmic rays fall on one line. We present here a potential explanation for this, by assuming that cosmic ray production is a byproduct of the generation of turbulence during the gravitational contraction of the Universe, i.e. structure formation. The model naturally explains why the maximum confinement energy is scale invariant, while reproducing BOTH the value of the maximum energy (~10^20 eV) and the overall extragalactic production rate, ~10^47 erg / Mpc^3 / year for a production spectral index of E^-2.3, from known cosmological parameters plus ONE free parameter, which is the fraction of gravitational energy transformed into turbulence and found to be close to its canonical expectation value. While the generic approach presented here can certainly not compete with detailed modeling of specific cosmic ray sources, it predicts the fractional energetic contribution of sources acting at different scales, and can thus serve as a theoretical prior for extragalactic cosmic ray production in Bayesian modeling of the large scale Galactic Magnetic Field from UHECR arrival directions.

Speaker: Jörg Paul Rachen (IMAPP / Radboud University Nijmegen)

JPR_Universal_talk.pdf

16:55 Theoretical uncertainties in extracting cosmic ray diffusion parameters: the boron to carbon ratio

PAMELA and, more recently, AMS-02, are ushering us into a new era of greatly reduced statistical uncertainties in experimental measurements of cosmic ray fluxes. In particular, new determinations of traditional diagnostic tools such as the boron to carbon ratio (B/C) are expected to significantly reduce errors on cosmic-ray diffusion parameters, with important implications for astroparticle physics, ranging from inferring primary source spectra to indirect dark matter searches. It is timely to stress, however, that the conclusions inferred crucially depend on the framework in which the data are interpreted as well as from some nuclear input parameters. We aim at assessing the theoretical uncertainties affecting the outcome, with models as simple as possible while still retaining the key dependences. We compare different semi-analytical, two-zone model descriptions of cosmic ray transport in the Galaxy: infinite slab/1D, cylindrical symmetry/2D with homogeneous sources, cylindrical symmetry/2D with inhomogeneous source distribution. We test for the effect of a primary source contamination in the boron flux by parametrically altering its flux, as well as for nuclear cross-section uncertainties. All hypotheses are compared via $\chi^{2}$ minimization techniques to preliminary results from AMS-02. We find that the major theoretical bias on the determination of the diffusion coefficient index $\delta$ (up to a factor two) is represented by the assumption that no injection of Boron takes place at the source. The next most important uncertainty is represented by cross-section uncertainties, which reach $\pm 20\%$ in $\delta$. As a comparison, nuclear uncertainties are more important than the shift in the best-fit when introducing a convective wind of velocity $>$30 km/s, with respect to a pure diffusive baseline model. Perhaps surprisingly, homogeneous 1D vs. 2D performances are comparable in determining diffusion parameters. An inhomogeneous source distribution marginally alters the central value of the diffusion coefficient normalization (at the 10%, $1\,\sigma$ level). However, the index of the diffusion coefficient $\delta$ is basically unaltered, as well as the goodness of fit. Our study suggests that, differently for instance from leptonic case, realistic modeling of the geometry of the Galaxy and of the source distribution are of minor importance to correctly reproduce B/C data at high-energies hence, to a large extent, for the extraction of diffusion parameters. The Ansatz on the lack of primary injection of Boron represents the most serious bias, and requires multi-messenger studies to be addressed. If that uncertainty could be lifted, nuclear uncertainties would still represent a serious concern, which degrade the systematic error on the inferred parameters to the 20\% level, or three times the estimated experimental sensitivity. In order to reduce this, a new nuclear cross-section measurement campaign is probably required.

Speaker: yoann genolini (LAPTh)

Presentation_TEXAS.pdf

17:15 Escape model: CR composition and diffuse gamma-ray and neutrino backgrounds

I review the escape model for Galactic cosmic rays (CRs) that reproduce over a wide range of energies all available experimental data for individual groups of CR nuclei. Then I discuss how the extragalactic proton component derived within this model can be explained by astrophysical sources, especially blazars. The diffuse neutrino and γ-ray fluxes produced by these CR protons interacting with gas inside their sources contribute the dominant fraction of both the isotropic γ-ray background and of the extragalactic part of the astrophysical neutrino signal observed by IceCube.

Speaker: Michael Kachelriess (NTNU)

17:35 A Uniformly Selected, All-Sky Optical AGN Catalog for UHECR Correlation

Studies discerning whether there is a significant correlation between ultra high energy cosmic ray (UHECR) arrival directions and optical AGN are hampered by the lack of a uniformly selected and complete all-sky optical AGN catalog. To remedy this, we are preparing such a catalog based on the 2MASS Redshift Survey (2MRS), a spectroscopic sample of $\sim 44,500$ galaxies complete to a K magnitude of 11.75 over 91% of the sky. We have analyzed the available optical spectra of these 2MRS galaxies ($\sim 80$% of the galaxies), in order to identify the AGN amongst them with uniform criteria. Although the selection is uniform, the spectra were taken with different instruments (the majority from four different observatories). We present not only the catalog but an assessment of its homogeneity and completeness. Correlations between this well-characterized catalog and UHECRs published by the Pierre Auger Observatory and its implications will also be discussed.

Speaker: Ingyin Zaw (NYU Abu Dhabi)

Texas_PosterPres_AGNCatalog.key

Texas_PosterPres_AGNCatalog.pdf

17:38 gap

Friday 18 December

08:30 → 09:00 Registration

09:00 → 10:45 Plenary talks

09:00 ESA gravitational wave observatory, eLISA and LISA Pathfinder

The talk will likely take place during the cruise of LISA Pathfinder to its final interplanetary orbit. LISA Pathfinder is the technology precursor of the Gravitational Wave (GW) observatory that ESA intends to launch as their 3rd large size mission within the current planning. The talk will review the status and the scientific objectives of the GW observatory, and of its reference mission eLISA, and will illustrate the instrumentation of LISA Pathfinder, its role within ESA's GW program, and the expected scientific return of its upcoming operations.

Speaker: Prof. Stefano Vitale (University of Trento)

Video

09:35 Exact solutions in astrophysics

There are over 1300 known exact solutions to Einstein’s equations. Part of these solutions found applications in astrophysics including the solar system, compact objects, and cosmology. These have offered some physical or mathematical insights into the systems under consideration. In this review talk, some characterizing notions about exact solutions will be outlined along with some examples. After a brief presentation of some neutron star models, the discussion will focus on inhomogeneous cosmological models and their applications. The related problem of averaging in relativity and cosmology will also be outlined.

Speaker: Prof. Mustapha Ishak (The University of Texas at Dallas)

ExactSolutionsInAstrophysics_Ishak_Final.pdf

Video

10:10 Exploring gravity in the strong field regime with high throughput X-ray measurements

High-time-resolution and spectroscopic observations of accreting collapsed objects in the X-ray range provide access to strong-field gravity, through measurements of the motions of matter orbiting a few gravitational radii away from black holes. Key predictions of strong field general relativity, such as relativistic epicyclic motions, precession, light bending and the presence and radius of an innermost stable circular orbit in the close vicinity of a black hole can be verified by making use of the two most important direct diagnostics, i.e. the relativistically broadened iron-lines and relativistic timescale variability, in particular the Quasi Periodic Oscillations. Both the low and high curvature regimes of strong field gravity can be probed by studying supermassive black hole in Active Galactic Nuclei and stellar-mass black holes in X-ray Binaries, respectively. This will afford testing general relativity against those alternative theories of gravity which predict deviations from General Relativity in the strong-field regime. To achieve these goals, very large area X-ray instrumentation with good spectral resolution is required. Prospects in this area of research will be surveyed.

Speaker: Prof. Luigi Stella (INAF - Osservatorio Astronomico di Roma)

Texas_Geneva_Stella.pdf

Video

10:45 → 11:20 Coffee break and poster session

11:20 → 12:30 Plenary talks

11:20 Heading into the abyss: X-ray spectral timing of accreting black holes

The innermost region of the accretion flow around X-ray bright, unobscured, Active Galactic and Black Hole Binaries (AGN and BHB) is being routinely mapped by X-ray spectral-timing of the reflection spectrum produced by irradiation of the accretion disc. The spin of the black hole can be determined by identifying the inner edge of the reflection region with the ISCO. The black hole in many of the objects studied then appears to be rapidly spinning. When an object has high spin and the corona lies close to the disc, as occurs some of the time for some sources, then most reflection originates within one gravitational radius of the event horizon.

Speaker: Prof. Andrew Fabian (University of Cambridge)

plenary_1120_Fabian.pdf

plenary_1120_Fabian.pptx

Video

11:55 Disks and jets

After reviewing the physics of jet formation by accreting black holes, I will present the results of recent 3D general relativistic magnetized fluid dynamics simulations and discuss the insights they give us into the disk-jet connection. I will finish by presenting the simulated spectra and images and the constraints on the near event horizon physics coming from the comparison to the observations of the supermassive black hole at the center of our galaxy.

Speaker: Alexander Tchekhovskoy (Uiversity of California Berkeley)

plenary_1155_Tchekhovskoy_Disks_and_jets.key.zip

plenary_1155_Tchekhovskoy_Disks_and_jets.pdf

Video

12:30 → 14:00 Lunch break

14:00 → 15:30 Cover: Highlights and conclusions

04_kunz.pdf

06_EarlyUniverse.pdf

11_GW.pdf

12_lensing.pdf

15_Binaries.pdf

15_PTA.pdf

19_VHE.pdf

20_Future.pdf

EarlyUniverseSummary.pdf

Texas2015_Session_Cosmic-Magnetic-Fields.pdf

15:30 → 15:35 Texas 2015 & Nepal

15:35 → 15:45 Texas 2017 - Cape Town

Speaker: Prof. Markus Boettcher (North-West University)

Boettcher_Texas2017.pdf

15:45 → 16:30 Coffee break and farewell