28th Texas Symposium on Relativistic Astrophysics

Dec 13, 2015, 4:00 PM → Dec 18, 2015, 5:10 PM 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, December 14

8:30 AM → 9:00 AM Registration

9:00 AM → 9:35 AM 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

9:00 AM Introduction

9:07 AM Welcome address by the Vice-Rector of the University of Geneva

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

9:15 AM Einstein's Swiss Years

Speaker: Prof. Jan Lacki (University of Geneva)

presentation_lacki.pdf

Video

9:35 AM → 10:45 AM Plenary talks

9:35 AM 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 AM 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 AM → 11:20 AM Coffee break and poster session

11:20 AM → 12:30 PM Plenary talks

11:20 AM 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 AM CMB spectral distortions

Speaker: Prof. Rashid Sunyaev

plenary_1155_Sunyaev.pdf

Video

12:30 PM → 2:00 PM Lunch break

2:00 PM → 3:45 PM 13 - Gamma-ray bursts

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

2:00 PM 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

2:21 PM 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

2:42 PM 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

3:03 PM 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

3:24 PM 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

2:00 PM → 3:45 PM 15 - Binaries: HMXB

Convener: Alessandro Papitto

2:00 PM 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

2:26 PM 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

2:52 PM 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

3:18 PM 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

2:00 PM → 3:45 PM 08 - Cosmic microwave background

Convener: Antony Lewis (University of Sussex)

2:00 PM 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

2:25 PM 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

2:45 PM 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

3:05 PM 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

3:25 PM 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

2:00 PM → 3:45 PM 06 - Early universe

Convener: Daniel G. Figueroa (CERN)

2:00 PM 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

2:21 PM 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

2:42 PM 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

3:03 PM 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

3:24 PM 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

2:00 PM → 3:45 PM 02 - Exact solutions

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

2:00 PM 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

2:21 PM 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

2:42 PM 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

3:03 PM 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

3:24 PM 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

2:00 PM → 3:45 PM 18 - Gal. accel. & pulsars: Galactic accelerators

Convener: Marco Tavani (INAF)

2:00 PM 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

2:20 PM 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

2:45 PM 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

3:05 PM 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

3:25 PM 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

2:00 PM → 3:45 PM 07 - Large scale structures

Convener: Vincent Desjacques

2:00 PM 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

2:21 PM 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

2:42 PM 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

3:03 PM 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

3:24 PM 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

2:00 PM → 3:45 PM 04 - Dark energy

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

2:00 PM 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

2:27 PM 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)

2:53 PM 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

3:19 PM 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

3:45 PM → 4:15 PM Coffee break and poster session

4:15 PM → 6:45 PM 13 - Gamma-ray bursts

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

4:15 PM 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

4:35 PM 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

4:55 PM 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

5:15 PM 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

5:35 PM 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

5:55 PM 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

5:58 PM 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

6:01 PM 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

6:04 PM gap

4:15 PM → 6:45 PM 15 - Binaries: HXMXB

Convener: Alessandro Papitto

4:15 PM 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

4:40 PM 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

5:05 PM 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

5:25 PM 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

5:45 PM 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

6:05 PM 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

6:20 PM 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

6:24 PM 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

6:27 PM gap

4:15 PM → 6:45 PM 08 - Cosmic microwave background

Convener: Antony Lewis (University of Sussex)

4:15 PM 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

4:35 PM 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

4:55 PM 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

5:15 PM 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

5:35 PM 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

5:55 PM gap

4:15 PM → 6:45 PM 06 - Early universe

Convener: Daniel G. Figueroa (CERN)

4:15 PM 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

4:35 PM 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

4:55 PM 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

5:15 PM 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

5:35 PM 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

5:55 PM 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

6:15 PM 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

6:35 PM gap

4:15 PM → 6:45 PM 02 - Exact solutions

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

4:15 PM 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

4:35 PM 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

4:55 PM 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

5:15 PM 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

5:35 PM 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

5:55 PM Discussion session on averaging and backreaction in cosmology

4:15 PM → 6:45 PM 18 - Gal. accel. & pulsars: Galactic accelerators

Convener: Marco Tavani (INAF)

4:15 PM 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

4:35 PM 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

4:55 PM 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

5:15 PM 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

5:35 PM 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

5:55 PM 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

6:15 PM 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

6:18 PM gap

4:15 PM → 6:45 PM 07 - Large scale structures

Convener: Vincent Desjacques

4:15 PM 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

4:35 PM 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

4:55 PM 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

5:15 PM 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

5:35 PM 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

5:55 PM 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

6:15 PM 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)

6:18 PM gap

4:15 PM → 6:45 PM 04 - Dark energy

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

4:15 PM 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

4:40 PM 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

5:05 PM 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

5:29 PM 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

5:53 PM 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

5:56 PM 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

5:59 PM 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

6:02 PM 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

6:05 PM 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)

6:08 PM 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

6:12 PM 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

6:15 PM 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

6:18 PM gap

Tuesday, December 15

8:30 AM → 9:00 AM Registration

9:00 AM → 10:45 AM Plenary talks

9:00 AM 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

9:35 AM 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 AM 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 AM → 11:20 AM Coffee break and poster session

11:20 AM → 12:30 PM Plenary talks

11:20 AM 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 AM 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 PM → 2:00 PM Lunch break

2:00 PM → 3:45 PM 13 - Gamma-ray bursts

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

2:00 PM 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

2:21 PM 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

2:42 PM 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

3:03 PM 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

3:24 PM gap

2:00 PM → 3:45 PM 15 - Binaries: ULX and LMXB

Convener: Alessandro Papitto

2:00 PM 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

2:25 PM 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

2:50 PM 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

3:20 PM 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

2:00 PM → 3:45 PM 16 - Black holes

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

2:00 PM 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

2:21 PM 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

2:42 PM 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

3:02 PM 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

3:22 PM 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

3:42 PM 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

2:00 PM → 3:45 PM 18 - Gal. accel. & pulsars: Pulsars

Convener: Marco Tavani (INAF)

2:00 PM 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

2:21 PM 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

2:42 PM 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

3:02 PM 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

3:22 PM 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

3:42 PM 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

2:00 PM → 3:45 PM 10 - Cosmic magnetic fields: Probes

Convener: Tina Kahniashvili

2:00 PM 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

2:25 PM 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

2:45 PM 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

3:05 PM 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

3:25 PM 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

2:00 PM → 3:45 PM 09 - Cosmic neutrinos

Convener: Julien Lesgourgues

2:00 PM 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

2:21 PM 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

2:42 PM 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

3:03 PM 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

3:24 PM 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

2:00 PM → 3:45 PM 19 - VHE & CR: Blazars and EBL

Convener: Teresa Montaruli

2:00 PM 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

2:21 PM 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

2:42 PM 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

3:03 PM 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

3:24 PM 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

2:00 PM → 3:45 PM 04 - Dark energy

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

2:00 PM 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

2:26 PM 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

2:53 PM 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

3:19 PM 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

3:45 PM → 4:15 PM Coffee break and poster session

4:15 PM → 6:45 PM .

4:15 PM → 6:45 PM 15 - Binaries: ULX and LMXB

Convener: Alessandro Papitto

4:15 PM 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

4:35 PM 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

4:55 PM 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

5:15 PM 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

5:35 PM 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

5:51 PM 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

6:08 PM 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

6:11 PM gap

4:15 PM → 6:45 PM 16 - Black holes

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

4:15 PM 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

4:40 PM 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

5:00 PM 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

5:20 PM 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

5:40 PM 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

6:00 PM 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

6:20 PM 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

6:23 PM 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

6:26 PM 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

6:29 PM gap

4:15 PM → 6:45 PM 18 - Gal. accel. & pulsars: Pulsars

Convener: Marco Tavani (INAF)

4:15 PM 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

4:35 PM 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

4:55 PM 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

5:15 PM 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

5:35 PM 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

5:55 PM 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

5:58 PM gap

4:15 PM → 6:45 PM 10 - Cosmic magnetic fields: Probes

Convener: Tina Kahniashvili

4:15 PM 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

4:35 PM 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

4:55 PM 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

5:15 PM 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

5:18 PM gap

4:15 PM → 6:45 PM 09 - Cosmic neutrinos

Convener: Julien Lesgourgues

4:15 PM 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

4:36 PM 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

4:57 PM 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

5:18 PM 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

5:39 PM 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

6:00 PM 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

6:20 PM 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

6:40 PM 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

6:43 PM 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

4:15 PM → 6:45 PM 19 - VHE & CR: Blazars and EBL

Convener: Elisa Prandini (University of Geneva)

4:35 PM 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

4:55 PM 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

5:15 PM 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

5:35 PM 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

5:55 PM 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

6:15 PM 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

6:35 PM 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)

6:38 PM gap

4:15 PM → 6:45 PM 03 - Modifications of gravity

Convener: Anne-Christine Davis (Cambridge University)

4:15 PM 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)

4:35 PM 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)

4:55 PM 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

5:25 PM 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

5:45 PM 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

6:10 PM 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

6:13 PM 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

6:16 PM 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

6:19 PM 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)

6:22 PM 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

6:25 PM 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

6:28 PM gap

7:30 PM → 9:30 PM Public talk

7:30 PM 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, December 16

8:30 AM → 9:00 AM Registration

9:00 AM → 10:45 AM Plenary talks

9:00 AM 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)

9:35 AM 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 AM 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 AM → 11:20 AM Coffee break and poster session

11:20 AM → 12:30 PM Plenary talks

11:20 AM 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 AM 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 PM → 2:00 PM Lunch break

2:00 PM → 3:45 PM 05 - Dark matter

Convener: Marco Cirelli (CEA/Saclay)

2:00 PM 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

2:25 PM 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

2:45 PM 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

3:05 PM 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)