# The Structure and Signals of Neutron Stars, from Birth to Death

Europe/Rome
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Description
This conference aims at bringing together people working in astrophysics of neutron stars, both on the theoretical and observational aspects. The following topics will be discussed : - Equation of state of dense matter, including hyperon, kaon and quark degrees of freedom - Neutrino emission and cooling of compact stars - Superconductivity-superfluidity - Constraints from EM observations - Transients - Gravitational wave emission - Models for Supernovae and for Gamma Ray Bursts - Magnetars.

This conference is co-organized by the  COST Action MP1304  (CompStar - Exploring fundamental physics with compact stars)

Participants
• Kenji Fukukawa
• Aida Kirichenko
• akram Dehghan niry
• Albino Perego
• Alessandro Drago
• Alessandro Parisi
• Alessandro Patruno
• Alfio Bonanno
• Alice Harding
• Andrea Lavagno
• Andrea Maselli
• Andrea Passamonti
• Andreas Bauswein
• Andreas Schmitt
• Andrei Beloborodov
• Andrew Mason
• Andrew Melatos
• Andrey Chugunov
• Andrzej Szary
• Anthea Francesca Fantina
• Anthony van Eysden
• Anton Biryukov
• Antonio Graziano Pili
• Antonio Pasqua
• Armen Sedrakian
• Arnau Rios Huguet
• Artur Polls
• avijit Kumar Ganguly
• Benjamin Owen
• Carlotta Pittori
• Cecilia Chirenti
• Charles Horowitz
• Christian David Ott
• Constança Providência
• Craig Heinke
• Cristiano Palomba
• Cristina Pallanca
• Cristobal Espinoza
• Daniele Viganò
• Dario Zappala
• David Edwin Alvarez Castillo
• David Keitel
• Deborah Aguilera
• Deepto Chakrabarty
• Dirk Rischke
• Dmitry Yakovlev
• Dubravko Klabučar
• Débora Menezes
• Edo Berger
• Elena Kantor
• Elena Pian
• Evgeni Kolomeitsev
• Farruh Atamurotov
• Federico Bernardini
• Fiorella Burgio
• Francesca Gulminelli
• François Aymard
• Friedrich Roepke
• Gabriele Taranto
• George Melikidze
• George Pappas
• Gergely Gabor Barnafoldi
• Giulia Pagliaroli
• Giuseppe Colucci
• Giuseppe Pagliara
• Gregory Ashton
• Grigor Alaverdyan
• Grégoire Martinon
• Hajime SOTANI
• Hamidreza Moshfegh
• Hans-Josef Schulze
• Hans-Thomas Janka
• Helena Pais
• Holger Stiele
• Irina Sagert
• Isaac Vidana
• Janusz Gil
• Jaroslaw Dyks
• Jason Dexter
• Jeroen Meidam
• JIAJIE LI
• Jorge Horvath
• Jose Pons
• Jérôme MARGUERON
• Jürgen Schaffner-Bielich
• Karl Wette
• Ken'ichi Nomoto
• Khaled Elshamouty
• Kostas Glampedakis
• Kosuke Sumiyoshi
• Kristian Petrik
• Laura Tolos
• Laurens Katgerman
• Leonardo Gualtieri
• Lubos Neslusan
• Luca Del Zanna
• Luca Franci
• Luciano Rezzolla
• Luigi Pilo
• Luigi Stella
• Manoneeta Chakraborty
• Manuel Linares
• Marcello Baldo
• Marcio Guilherme Bronzato de Avellar
• Marco Drago
• Marco Pierbattista
• Maria Chernyakova
• Maria Concetta Tringali
• Maria Naeem
• Mark Alford
• Massimiliano De Pasquale
• Massimiliano Razzano
• Massimo Della Valle
• Matthias Hempel
• Michael Gabler
• Michael Jasiulek
• Michalis Agathos
• Miguel Gullón Juanes
• Mikhail Gusakov
• Miroslav Shaltev
• Mohsen Bigdeli
• Monika Sinha
• Muneeb ur Rahman
• Nanda Rea
• Nathalie Degenaar
• Niccolo' Bucciantini
• Nicolae Sandulescu
• Nicolas Chamel
• Nitesh Thapa
• Nobutoshi Yasutake
• Oleg Korobkin
• Oliver Just
• patrick osei
• Paul Scholz
• Paulo Freire
• Pawel Danielewicz
• Pawel Haensel
• Peter Senger
• Peter Gonthier
• Peter Shternin
• Pierre Pizzochero
• Plamen Fiziev
• Rafael Camargo Rodrigues de Lima
• Ramandeep Gill
• RANJAN SHARMA
• Ricard Ardevol Pulpillo
• Ricardo Heras
• Robert Archibald
• Roberto Mignani
• Rodrigo Souza
• Roshan Sellahew
• Rudiney Casali
• Sachin Kaothekar
• Scott Ransom
• Sebastien Guillot
• Sergey Popov
• Sergey Zharikov
• Shuta Tanaka
• Silvia Chiacchiera
• Sofie Fehlmann
• Somayeh Goudarzi
• Stefan Gmuca
• Stefan Schramm
• Stefanos Tsiopelas
• Sumiko Kida
• Tania Regimbau
• Tanja Hinderer
• Tetiana Nikolaiuk
• Thomas Tauris
• Toshiki Maruyama
• Toshio Nakano
• Tsuneo Noda
• Ulrich R.M.E. Geppert
• Vanessa Graber
• Veronica Dexheimer
• Volodymyr Kryvdyk
• Wynn Ho
• Xavier Viñas
• Yuichiro Sekiguchi
• Zurab Berezhiani
Support
• Monday, 24 March
• 09:00 11:10
Plenary session 1
Convener: Constança Providência (University of Coimbra)
• 09:00
Welcome and introduction 10m
• 09:10
The Equation of State of Neutron Star Matter 40m
The main features of the EOS of neutron star matter are reviewed, comprising nucleonic, hyperonic, and quark matter contributions. The focus in on the Brueckner-Hartree-Fock theoretical method, but also other approaches will be regarded.
Speaker: Dr Hans-Josef Schulze (INFN Sezione di Catania)
• 09:50
Constraints on the Equation of State of Nuclear Matter from Heavy-Ion Collisions and from Structure 40m
Constraints on the nuclear equation of state, following from heavy ion collisions and from structure, are reviewed. The collisions produce matter transiently reaching densities few times the normal. Isolating observables testing such densities is challenging, though, and interpretation of those observables suffers from theoretical uncertainities. Structure observables can be generally accurately determined, but test only densities up to normal and are sensitive to poorly controlled microscopic effects. In spite of the difficulties, through gradual progress, it became possible to constrain the equation of state of symmetric matter at densities few times the normal, using anisotropic collective flow and kaon yields as crucial observables. Nuclear incompressibility was constrained using energies of giant monopole resonances, excited through alpha scattering. The current laboratory efforts concentrate on the role of neutron-proton asymmetry in the nuclear equation of state. Advances made on the collision and structure side, including studying of mass systematics, produced constraints on symmetry energy at subnormal densities. Limited progress, though, was made so far with regard to the symmetry energy at supranormal densities, important for extrapolations from nuclei to neutron stars. The greatest promise among observables is held by the charged pion yields which test neutron-proton composition of high-density matter in collisions, regulated itself by the high-density symmetry energy.
Speaker: Prof. Pawel Danielewicz (East Lansing, MSU (USA))
• 10:30
Strangeness in Compact Stars 40m
In the dense interior of compact stars the composition might change considerably. Due to weak equilibrium in neutron star matter particles carrying strangeness can appear changing the overall global properties as well as the transport properties of compact stars. The new pulsar mass limit of two solar masses gives new information on the presence of strange matter in the core of compact stars. New degrees of freedom, as strangeness, usually soften the nuclear equation of state, thereby reducing the maximum mass possible. Certain classes of microscopic models including hyperons face the problem that the maximum mass is well below the two solar mass limit, which is the so called 'hyperon puzzle', while other nuclear models describing hypernuclear properties result in neutron star masses of two solar masses or more. As a possible reconciliation of the hyperon puzzle, the presence of strange quark matter stabilizing the core of neutron stars have been invoked. The implications of the new pulsar mass limit on the parameters of the hypernuclear models as well as of quark matter models will be discussed in the presentation.
Speaker: Dr Juergen Schaffner-Bielich (Institut fuer Theoretische Physik, Goethe Universitaet, Frankfurt)
• 11:10 11:40
Coffee break 30m
• 11:40 13:00
Plenary session 2
Convener: Constança Providência (University of Coimbra)
• 11:40
Hybrid stars: how can we identify them ? 40m
At high pressure, nuclear matter will undergo a transition to quark matter, so sufficiently heavy neutron stars may really be hybrid stars'' with quark matter cores. We discuss possible signatures of the presence of a quark matter core, such as characteristics of the mass-radius relation, and the allowed range of values of the spin frequency, which is sensitive to quark matter in the core via the r-mode spindown mechanism. We also present a new form of dissipation of r-modes that is expected to occur in hybrid stars: "phase conversion dissipation".
Speaker: Prof. Mark Alford (Washington University in St. Louis, USA)
• 12:20
Exploring dense nuclear matter with heavy-ion collisions 40m
Nucleus-nucleus collisions provide a unique opportunity to create and to investigate dense nuclear matter in the laboratory. These experiments address fundamental aspects of strong-interaction physics: the nuclear equation-of-state at high baryon densities, the in-medium modifications of hadrons, and the phase transition from hadronic to partonic degrees of freedom. These phenomena play an important role for the dynamics of core-collapse supernovae, and for the structure of neutron stars. Nuclear matter densities of up to three times saturation density can be produced in heavy-ion collisions at GSI in Darmstadt/Germany. Experiments found evidence for a soft nuclear equation of state using kaons as diagnostic probe. Moreover, the yield and the emission pattern of strange mesons indicate that the properties of kaons and antikaons are modified in dense nuclear matter. Even more extreme conditions will be created in heavy-ion collisions at the future Facility for Antiproton and Ion Research (FAIR) in Darmstadt. Here, the goal of the experiments is to explore the QCD phase diagram in the region of the highest baryon densities, where a transition to quark matter is expected. This approach is complementary to the experiments at RHIC and LHC, where matter at very high temperatures but vanishing net baryon density is produced. The future heavy-ion program at FAIR will be discussed.
Speaker: Prof. Peter Senger (GSI Helmholtzzentrum für Schwerionenforschung)
• 13:00 14:30
Lunch break 1h 30m
• 14:30 16:30
Afternoon session - Parallel A
Convener: Christian Ott (C)
• 14:30
Direct formation of millisecond pulsars from rotationally delayed accretion-induced collapse of massive white dwarfs 20m
Millisecond pulsars (MSPs) are believed to be old neutron stars, formed via type~Ib/c core-collapse supernovae, which have subsequently been spun up to high rotation rates via accretion from a companion star in a highly circularised low-mass X-ray binary. The recent discoveries of Galactic field binary MSPs in eccentric orbits, and mass functions compatible with that expected for helium white dwarf companions, PSR J2234+06 and PSR J1946+3417, therefore challenge this picture. Here we present a hypothesis for producing this new class of systems, where the MSPs are formed directly from a rotationally-delayed accretion-induced collapse of a super-Chandrasekhar mass white dwarf. We compute the orbital properties of the MSPs formed in such events and demonstrate that our hypothesis can reproduce the observed eccentricities, masses and orbital periods of the white dwarfs, as well as forecasting the pulsar masses and velocities. Finally, we compare this hypothesis to a triple star scenario.
Speaker: Dr Paulo Freire (MPI Bonn)
• 14:50
Formation of Neutron Stars from the ONeMg Core of Super-AGB Stars 20m
The stellar mass range (8 - 10) Msun corresponds to the most massive AGB stars and the most numerous massive stars. We study the transition from super-AGB star to massive star and find that a propagating neon-oxygen burning shell is common to both the most massive electron capture supernova (EC-SN) progenitors and the lowest mass iron-core collapse supernova (FeCCSN) progenitors. Of the models that ignite neon burning off-center, the 9.5 Msun model will evolve to an FeCCSN after the neon-burning shell propagates to the center. The neon-burning shell in the 8.8 Msun model, however, fails to reach the center as the URCA process and an extended region of low Y_e in the outer part of the core begin to dominate the late evolution; the model evolves to an EC-SN. This is a new evolutionary path to EC-SN in addition to that from S-AGB stars undergoing thermal pulses. We show that the two evolutionary fates (EC-SN and FeCCSN) are separated by the dynamics of the neon and oxygen burning shells and the behavior of the URCA process. We have also computed an 8.75 Msun super-AGB star through its entire thermal pulse phase until electron captures on 20Ne begin at its center, and examine the differences between the pre-SN evolution and progenitor structure of the 8.75 and 8.8 Msun models. We present two supernova progenitor structures for EC-SNe (a super-AGB star and a failed massive star') and one FeCCSN progenitor structure from a 12 Msun star. We discuss how the different pathways to collapse affect the pre-supernova structure and compare our results to the observed neutron star mass distribution. Finally, we demonstrate the light curves of EC-SNe from super-AGB stars to compare the observation including the Crab supernova 1054.
Speaker: Ken'ichi Nomoto
• 15:10
Ultra-stripped Type Ic supernovae from close binary evolution 20m
Recent discoveries of weak and fast optical transients raise the question of their origin. We investigate the minimum ejecta mass associated with core-collapse supernovae (SNe) of Type Ic. We show that mass transfer from a helium star to a compact companion can produce an ultra-stripped core which undergoes iron core collapse and leads to an extremely fast and faint SN Ic. In this Letter, a detailed example is presented in which the pre-SN stellar mass is barely above the Chandrasekhar limit, resulting in the ejection of only ~0.05-0.20 M_sun of material and the formation of a low-mass neutron star. We compute synthetic light curves of this case and demonstrate that SN 2005ek could be explained by our model. We estimate that the fraction of such ultra-stripped to all SNe could be as high as 0.001-0.01. Finally, we argue that the second explosion in some double neutron star systems (for example, the double pulsar PSR J0737-3039B) was likely associated with an ultra-stripped SN Ic.
Speaker: Dr Thomas Tauris (MPIfR Bonn)
• 15:30
Spectral signatures of super-luminous supernovae powered by magnetars and black holes 20m
Wide-field optical surveys have discovered a population of super-luminous supernova explosions in the past several years, including some where it is difficult to explain the light curve shape using energy deposition from radioactive decay. Many of these events can be explained by a model in which a rapidly rotating magnetar forms in the explosion and deposits its spindown energy into the supernova ejecta. I will show that the injected energy could also be provided by fallback accretion of material which remains bound to the proto-neutron star. At late times, the central engine in these models should shine through the supernova ejecta, significantly affecting the observed properties. I will discuss calculations of the ejecta opacity as a function of waveband and time for the magnetar model, and the resulting predictions for multi-wavelength observations of super-luminous supernovae.
Speaker: Dr Jason Dexter (UC Berkeley)
• 15:50
Neutrino-driven wind from the aftermath of binary neutron star mergers 20m
Binary neutron star mergers are among the most extreme events happening in the Universe. These very powerful events are expected to release large amounts of energy in form of neutrinos, gravitational waves and electromagnetic radiation, together with the ejection of a small fraction of their original mass. In particular, they are expected to be sites for r-process nucleosynthesis, as well as very promising candidates to power short-hard gamma-ray bursts (GRBs) and/or the newly discovered macro/kilo-novae. In this talk I will present results from 3D simulation of the aftermath of a binary neutron star merger. The (Newtonian) dynamics of the disk will be investigated, as well as the neutrino emission coming from the central object and the inner part of the accreting torus. The neutrino emission is modeled by an advanced spectral leakage scheme. It includes a model for neutrino diffusion in the optically thick regime, and takes into account neutrino absorption in the optically thin regions of the disk. Results regarding the production of a baryonic neutrino-driven wind will be discuss, with a special emphasis on its properties related with nucleosynthesis (electron fraction, entropy, velocity) and with the possibility to power a short GRB (wind geometry, baryonic pollution).
Speaker: Dr Albino Perego (TU Darmstadt, Institut für Kernphysik Theoriezentrum)
• 14:30 16:30
Afternoon session - Parallel B
Convener: Isaac Vidana (University of Coimbra, Portugal)
• 14:30
The symmetry energy and neutron star properties 20m
The effect of the symmetry energy on several properties of neutron stars is discussed. First, we analyze the effect of the symmetry energy on the pasta phase. It is shown that the size of the pasta clusters, number of nucleons and the cluster proton fraction depend on the density dependence of the symmetry energy: a small L gives rise to larger clusters. The influence of the equation of state at subsaturation densities on the extension of the inner crust of the neutron star is also discussed. We then discuss effect of the density dependence of the symmetry energy on the strangeness content of neutron stars. It is found that charged (neutral) hyperons appear at smaller (larger) densities for smaller values of the slope parameter L. A linear correlation between the radius and the strangeness content of a star with a fixed mass is also found. Finally we analyse the effect of the symmetry energy on the evolution of a proto-neutron star with a kaon condensate.
Speaker: Prof. C. Providência (University of Coimbra)
• 14:50
Phase diagram of nuclear matter in the stellar medium 20m
Dense matter as it can be found in core-collapse supernovae and neutron stars is expected to exhibit different phase transitions which impact the matter composition and equation of state, with important consequences on the dynamics of core-collapse supernova explosion and on the structure of neutron stars. In this talk we will address the specific phenomenology of two of such transitions, namely the crust-core solid-liquid transition at sub-saturation density, and the possible strange transition at super-saturation density in the presence of hyperons’ degrees of freedom. The opening of hyperons degrees of freedom at the super-saturation densities corresponding to the neutron stars core modifies the equation of state, with important consequences on the total mass and radius of the star, as well as possible effects on the neutrino dynamics. The conditions of existence of such a phase transition and its observable consequences will be discussed in the framework of the self-consistent relativistic as well as non-relativistic mean-field approach. The need of constraints from laboratory data will be highlighted. Concerning the neutron star crust-core phase transition at zero and finite temperature, a Nuclear Statistical Equilibrium model will be presented including in-medium modifications of the clusters self-energies consistently calculated from realistic nuclear effective interactions. Some quantitative results relevant for the structure of neutron star crusts and the supernova dynamics will be shown.
Speaker: Prof. Francesca Gulminelli (LPC and Univ.of Caen)
• 15:10
Role of superfluidity close to the neutron drip line 20m
Exotic and drip-line nuclei as well as nuclei immersed in a low-density gas of neutrons in the inner crust of neutron stars are systematically investigated with respect to their neutron pairing properties. This is done using Skyrme density-functional and different pairing forces such as a density-dependent contact interaction and a separable form of a finite-range Gogny interaction. Hartree-Fock-Bogoliubov (HFB) and Bardeen-Cooper-Schrieffer (BCS) theories are compared. It is found that neutron pairing is reduced towards the drip line while overcast by strong shell effects. Furthermore, resonances in the continuum can have an important effect counterbalancing the tendency of reduction and leading to a persistence of pairing at the drip line.
Speaker: Dr Jerome Margueron (IPN Lyon, France)
• 15:30
Clusterized nuclear matter in the (proto-)neutron star crust and the symmetry energy 15m
Though generally agreed that the symmetry energy plays a dramatic role in determining the structure of neutron stars and the evolution of core-collapsing supernovae, little is known in what concerns its value away from normal nuclear matter density and, even more important, the correct definition of this quantity in the case of unhomogeneous matter. Indeed, nuclear matter traditionally addressed by mean-field models is uniform while clusters are known to exist in the dilute baryonic matter which constitutes the main component of compact objects outer shells. In the present work we investigate the meaning of symmetry energy in the case of clusterized systems and the sensitivity of the proto-neutron star composition and equation of state to the effective interaction. To this aim an improved Nuclear Statistical Equilibrium (NSE) model is developed, where the same effective interaction is consistently used to determine the clusters and unbound particles energy functionals in the self-consistent mean-field approximation. In the same framework, in-medium modifications to the cluster energies due to the presence of the nuclear gas are evaluated. We show that the excluded volume effect does not exhaust the in-medium effects and an extra isospin and density dependent energy shift has to be considered to consistently determine the composition of subsaturation stellar matter. The symmetry energy of diluted matter is seen to depend on the isovector properties of the effective interaction, but its behavior with density and its quantitative value are strongly modified by clusterization.
• 15:45
SU(3) symmetric hypernuclear matter and related stellar properties 15m
Based on the SU(3) symmetry group, we fix the hyperon-meson coupling constants and constrain them to experimental nuclear matter results and astrophysical observations. We then study the effects of meson-hyperon coupling constants on the onset of hyperons in dense nuclear matter. While the discovery of massive pulsars PSR J1614-2230 and PSR J0348+0432 points towards a very stiff equation of state at very large densities, results from heavy ion collisions point in opposite direction for densities below five times the nuclear saturation density. We study some well known quantum hadrodynamics parametrizations and see that most of them cannot satisfy both types of constraints.
Speaker: Dr Debora Menezes (Universidade Federal de Santa Catarina)
• 16:00
New approach to an effective density dependence within an advanced relativistic mean-field theory. 15m
Recent progress in astronomical observations, namely accurate estimation of the mass of the pulsars J1614-2230 and J0348+0432, which yields values around 2 M_sol, demands that any reliable nuclear equation of state (EoS) should be able to reproduce these results. Common feature of models that include hyperon degrees of freedom, kaon condensates or other forms of exotic hadronic matter, is softening of the EoS along with the appearance of such particles. The density dependent relativistic hadron field (DDRHF) theory is no exception. To help improve, or overcome this issue, we present several new approaches to the effective density dependence of DDRHF models, which include an introduction of 2-parametric class of density dependent functions, as well as mapping of Fock exchange terms onto the mean-field theory. To estimate reliable parametrizations, we made fits of our models to the more fundamental Dirac-Brueckner-Hartree-Fock (DBHF) calculations, with the use of above techniques. Our results show promising improvements with respect to the compact star physics.
Speaker: Kristian Petrik (Institute of Physics, Slovak Academy of Sciences)
• 16:15
Dirac density functional for dense matter 15m
The exchange part of energy density of the linear Dirac-Hartree-Fock (DHF) model in dense matter is evaluated in a parameter-free closed form and expressed as density functional. After the rearranging terms the relativistic mean-field approach with density-dependent couplings may be recovered with density dependence coming from the Fock interaction. The formalism developed, is then extended to the nonlinear DHF approximation with field self-couplings allowed. The nonlinear self-interactions result in essential density dependence of effective couplings that is decoupled from the Fock one. Finally, the model is applied to investigate the properties of dense stellar matter.
Speaker: Stefan Gmuca (Institute of Physics, Slovak Academy of Sciences)
• 16:30 17:00
Coffee break 30m
• 17:00 18:40
Evening session - Parallel A
• 17:00
Inhomogeneous phases in dense strongly interacting matter - a generic phenomenon? 20m
Calculations within QCD-inspired models as well within QCD in the large-N_c limit show that dense quark matter features inhomogeneous phases. The order parameter for chiral symmetry breaking varies periodically, in the form of a chiral density wave ("chiral spiral") or in the functional form of a Jacobi elliptic function. In this talk, I will demonstrate that this phenomenon also occurs in an effective chiral model with purely hadronic degrees of freedom. The parameters of the model are adjusted to give a reasonable fit of hadron vacuum properties. The model is also able to reproduce nuclear matter saturation properties. We find that, above a density of about 2.4 times the nuclear matter ground state density, an inhomogeneous phase sets in, where the chiral order parameter varies in the form of a chiral density wave. Thus, inhomogeneous phases seem to be a generic feature of high-density strongly interacting matter.
Speaker: Prof. Dirk Rischke (Institut für Theoretische Physik Johann Wolfgang Goethe-Universität)
• 17:20
Compact stars and general constraints on exotic phases 20m
With the measurements of two-solar-mass neutron stars the question of how to reconcile the existence of large masses with the possibility of more exotic compact objects like hyper stars and hybrid stars has gained major importance. In order to address this point theoretical approaches to model stars containing quarks as well as nucleons and hyperons are discussed, also considering the general phase structure and types of phase transitions in dense and hot strongly interacting matter. Possible limits on the amount of hyperon and quark matter are investigated. Within the same ansatz results from other areas of strong interaction physics, especially heavy-ion physics and lattice QCD simulations, are considered that might constrain non-nucleonic contributions to compact stars. In this context seemingly conflicting results from lattice simulations and model studies regarding quark interactions can be understood by separately analyzing the hadronic and quark phases.
Speaker: Prof. Stefan Schramm (Frankfurt Institute for Advanced Studies Johann Wolfgang Goethe Universität)
• 17:40
Equation of State for Hybrid Compact Stars 20m
I model hybrid compact stars making use of a self-consistent equations of state. In this approach, the degrees of freedom change from hadrons to quarks in a self-consistent way. This means that the particles appear, in principle, in arbitrary proportions with the interactions leading to the correct behavior for low, respectively high, densities and temperatures. Chiral symmetry restoration and deconfinement phase transitions range from smooth crossovers to sharp first order phase transitions. Effects of strong magnetic fields are analyzed and the achievement of two solar masses stars is discussed.
Speaker: Prof. Veronica Dexheimer (Kent State University)
• 18:00
Constraining the Field Correlator Method by Neutron Star observations 20m
The Field Correlator Method provides an approximation of the full Quantum Chromodynamics Equation of State (EoS) for quark matter, which is parametrized in terms of the gluon condensate and the large distance quark-antiquark potential. This EoS can be confronted with the hadronic EoS to analyze the phase transition from nuclear to quark matter, thus providing a simple framework to describe the interior of a Neutron Star. In particular, it is discussed how recent observational data on heavy neutron star masses put some physical constraints on the two parameters of the model.
Speaker: Dr Dario Zappalà (INFN Cezione di Catania)
• 18:20
Pasta structures in quark-hadron phase transition by non-local NJL model 20m
We study the quark-hadron phase transition with the finite size effects for neutron star matter. Generally, non-uniform structures appear in the phase transition of multi-component system. Namely, we call them as the pasta structures. In this study, the properties of the mixed phase are clarified by considering the finite size effects. We find that, if the surface tension is strong, the EOS becomes to be close the one with the Maxwell condition, though we adopt the Gibbs conditions. We adopt the non-local NJL model, but the result is qualitatively same with the one with a simple bag model. Hence, we conclude that the finite size effects on EOS have universality. We also find that the mass-radius relations by the EOS are consistent with the observations.
Speaker: Prof. Nobutoshi Yasutake (Chiba Institute of Technology)
• 17:00 18:30
Evening session - Parallel B
Convener: Scott Ransom (NRAO, USA)
• 17:00
Population synthesis of radio and gamma-ray normal, isolated pulsars using Markov Chain Monte Carlo 15m
We present preliminary results of a population statistics study of normal pulsars (NP) from the Galactic disk using Markov Chain Monte Carlo techniques. The model parameters are varied to maximize the log of the likelihood obtained from the comparisons of two and one dimensional distributions of radio and gamma-ray pulsar characteristics. The computer code simulates neutron stars at birth using Monte Carlo procedures and evolves them to the present assuming initial spatial, kick velocity, magnetic field, and period distributions. Pulsars are spun down to the present and given radio and gamma-ray emission characteristics with empirical radio and gamma-ray luminosity models. We explore a magnetic inclination angle alignment model as well as a magnetic-field decay model. A comparison group of radio NPs detected in ten-radio surveys normalizes the simulation by adjusting the model radio luminosity to match the supernova rate. We include pulsars in the Fermi second pulsar catalog. We present results comparing the simulated and detected distributions of radio and gamma-ray NPs along with a confidence region in the parameter space of the assumed models. We express our gratitude for the generous support of the Michigan Space Grant Consortium, National Science Foundation (RUI), and the NASA Astrophysics Theory and Fundamental Program.
Speaker: Prof. Peter Gonthier (Hope College)
• 17:15
Population synthesis of Isolated Neutron Stars 15m
The neutron star zoo has witnessed a continuous increase in the number of species during the last decades, as more sensitive instruments were developed, in particular in the high energy band (Fermi-LAT, XMM-Newton, Chandra...). Despite the observational diversity, a consistent theory must be able to explain the different manifestations in terms of different initial conditions or evolutionary paths. By means of Population Synthesis techniques applied to the population of isolated Neutron Stars, we aim at giving a unified description of the many faces of neutron stars. These techniques, based on Monte Carlo methods, consist in the simulation of a whole population of sources. Once a population is created, for each evolutionary model, we can look for the optimal parameter combination that reproduces the observed distributions. Despite the numerous uncertainties and the poor statistics, which results in degeneracy in the parameter space, we show that performing a multiband study of different subpopulations (radio pulsars, X-ray pulsars, gamma-ray pulsars and bursters), some constraints can be obtained.
Speaker: Miguel Gullón (University of Alicante)
• 17:30
Evolution of relativistic binary systems 15m
We present a general picture for the evolution of relativistic binary systems, including those recycling NSs to millisecond periods, and those ending in “redbacks” and “black widow” systems . The theoretical framework includes all physical effects though to be relevant for the description of mass transfer $\dot{M}$ namely accretion, evaporation of matter by pulsar irradiation and X-rays irradiation feedback. We follow evolutionary tracks and show that the interplay of $\dot{M}$ and orbital evolution, calculated with a fully implicit code, is capable of explaining the whole variety of observed binary systems. In particular, we show that “redback” systems are just a transitory (but very long) stage driven by an oscillatory mass transfer. Finally, we demonstrate that very high masses $\geq 2 M_{\odot}$ are a natural outcome and match the observed values reported recently for the NS in these systems.
Speaker: Jorge Horvath (I)
• 18:00
Energy transformations in the birth of neutron stars 15m
Millisecond pulsars, radio pulsars, and magnetars are distinct classes of neutron stars that currently exhibit different periods, magnetic fields and space velocities. In my talk, I speculate with the idea that these current properties of neutron stars could have had similar values during the birth of these stars. I develop a relatively simple model based on the assumption that neutron stars experienced three abrupt physical changes at the end of their birth, which could have been originated in birth magneto-rotational instabilities: an increase in period from the initial value to the current value, implying a change of rotational energy; an exponential decay of its magnetic field from the initial value to the current surface value, implying a change of radiative energy; and finally, an increase of space velocity from the initial value to the current value, implying a change of kinetic energy. These birth energy changes are assumed to be connected by an energy conversion in which a radiation loss and an increase of kinetic energy occur at the expense of a rotational energy loss. According to this model, If the assumed energy conversion occurs in times of order 10^(-4) s then neutron stars are born with magnetic fields in the range of 10^(15)-10^(16) G and initial periods in range 1-20 ms. This means that neutron stars are born with magnetic fields typical of magnetars and periods typical of millisecond pulsars.
Speaker: Dr Ricardo Heras (University College London)
• 18:15
Follow-up searches for continuous gravitational waves 15m
Isolated neutron stars are possible sources of continuous gravitational waves. If the source parameters are known, a putative signal can be searched at negligible computing cost. For unknown source parameters, the weakness of the expected signal combined with the large parameter space to search yields an unfeasible computing cost for fully coherent search techniques. Therefore advanced semi-coherent search methods have been developed, e.g., StackSlide and the Hough transform. These methods are currently used in distributed computing environments such as Einstein@Home. The searches narrow down the parameter space around possible candidates, which then need to be followed up. We present a general two-stage method based on numerical optimization (NOMAD), which allows for the fully coherent follow-up of such candidates on all of the available data at a feasible computing cost. We describe the practical application of this procedure on the candidates from a semi-coherent Hough-transform all-sky search.
Speaker: Dr Miroslav Shaltev (Albert Einstein Institute, Hannover)
• Tuesday, 25 March
• 09:00 11:00
Plenary session 3
Convener: Armen Sedrakian (Frankfurt University)
• 09:00
Vela Pulsar Glitches and Nuclear Superfluidity 40m
At the endpoint of stellar evolution, pulsars are spinning extremely rapidly with periods ranging from milliseconds to seconds and delays of a few milliseconds per year at most, thus providing the most accurate clocks in the universe. Nevertheless, some pulsars exhibit sudden decreases of their spin period. Because it was the first observed pulsar to exhibit such “glitches”, Vela has become the testing ground for glitch theories. Sudden pulsar spin-ups have long been thought to be the manifestation of a neutron superfluid permeating the crustal layers of these dead stars [1]. However, recent calculations indicate that this scenario is unrealistic [2,3] because neutrons are very strongly coupled to the crust due to non-dissipative entrainment effects [4]. These effects, which were previously ignored, not only challenge the interpretation of Vela pulsar glitches but also suggest that a revision of the interpretation of other observed neutron-star phenomena might be necessary. [1] P. W. Anderson and N. Itoh, Nature 256, 25 (1975). [2] N. Andersson, K. Glampedakis, W. C. G. Ho, and C. M. Espinoza, Phys. Rev. Lett. 109, 241103 (2012). [3] N. Chamel, Phys. Rev. Lett. 110, 011101 (2013). [4] N. Chamel, Phys. Rev. C85, 035801 (2012).
Speaker: Prof. Nicolas Chamel (Universitè Libre de Bruxelles, Belgium)
• 09:40
Theory of cooling neutron stars 40m
Cooling neutron stars may serve as natural laboratories of superdense matter in their interiors. We discuss current theories of neutron star cooling. We outline the main regulators of the cooling such as the equation of state, neutrino emission mechanisms, heat capacity and superfluidity in superdense stellar cores as well as the properties of heat-blanketing envelopes of neutron stars. Next we describe which information on neutron star parameters and physical properties of superdense matter can be inferred from observations of cooling neutron stars, and summarize the results and perspectives of such investigations.
Speaker: Prof. Dmitry Yakovlev (IOFFE Institute)
• 10:20
Superfluidity and superconductivity in neutron stars 40m
I will review some key aspects of the physics of neutron star superfluidity and superconductivity, which play an important role in the phenomena of pulsar timing noise and rotational glitches. New results will be presented from quantum mechanical Gross-Pitaevskii simulations of vortex avalanches in a pinned, decelerating superfluid, which show the correlated nature of vortex motion during glitches explicitly for the first time and provide a robust explanation of certain aspects of glitch statistics. Future gravitational wave experiments probing neutron star superfluidity and superconductivity will be evaluated critically and related to fundamental open questions concerning the physics of bulk nuclear matter.
Speaker: Dr Andrew Melatos (University of Melbourne, Australia)
• 11:00 11:30
Coffee break 30m
• 11:30 12:50
Plenary session 4
Convener: Armen Sedrakian (Frankfurt University)
• 11:30
Neutron Star Binary Mergers as the Progenitors of Short GRBs 40m
While short-duration gamma-ray bursts (GRBs) have long been suspected to result from the mergers of compact object binary mergers, it is only over the past few years that observational data have been available. In this talk I will present the results of several detailed studies of short GRBs and their environments which demonstrate a connection to neutron star binary mergers, and which can be used to shed light on the electromagnetic counterparts of Advanced LIGO/Virgo sources.
Speaker: Prof. Edo Berger (Harvard, USA)
• 12:10
Nuclear Physics at Two Kiloparsecs with Millisecond Pulsars 40m
The central densities of neutron stars are the highest known in the Universe, so measurements probing the interiors of radio pulsars, or even just their masses and radii, can give us unique insights into the physics of matter at extreme densities. The discovery of several interesting new pulsars as well as improved instrumentation has finally allowed us to start measuring the masses of the rapidly spinning millisecond pulsars. High-precision radio timing measurements of relativistic parameters, like the Shapiro Delay, have yielded several neutron stars near 2 solar masses, while optical observations of some "black widow" radio pulsars have indicated potentially even more massive neutron stars. Such systems strongly constrain the equation of state of neutron star matter and a variety of other topics in physics/astrophysics. New radio telescopes like MeerKAT, FAST, and the SKA will provide many new pulsars and corresponding new mass measurements.
Speaker: Scott Ransom (National Radio Astronomy Observatory)
• 12:50 14:30
Lunch break 1h 40m
• 14:30 16:30
Afternoon session - Parallel A
Convener: Dmitry Yakovlev (IOFFE Inst., San Petersburg)
• 14:30
Transport coefficients of nuclear matter in neutron star cores in the BHF framework 20m
We calculate shear viscosity and thermal conductivity of dense asymmetric nuclear matter in the neutron star cores. Nuclear interaction is treated in the framework of non-relativistic Brueckner-Hartree-Fock formalism. The full Argonne v18 potential with addition of the Urbana IX effective three-body forces is used. In general, in-medium effects at two-body level lead to increase of the transport coefficients mainly due to decrease of the carriers’ effective masses. However, we found that use of the Urbana IX three-body force leads to decrease in the kinetic coefficients with the respect to two-body case. The results of our calculations [1] are compared with the electron and muon transport coefficients and with results of other authors. [1] P.S. Shternin, M. Baldo, and P.Haensel, PRC, 88, 065803 (2013)
Speaker: Peter Shternin
• 14:50
Transport coefficients in superfluid neutron stars 20m
We study the shear and bulk viscosity coefficients as well as the thermal conductivity as arising from the collisions among phonons in superfluid neutron stars. We use effective field theory techniques to extract the allowed phonon collisional processes, written as a function of the equation of state of the system. We analyze the shear viscosity taking into account the contribution of superfluid phonons to the viscosity, both in their hydrodynamical and ballistic regime. We compare to recent calculations of the shear viscosity from electron collisions and comment on the possible consequences for r-mode damping in superfluid neutron stars. Moreover, we find that phonon collisions give the leading contribution to the bulk viscosities in the core of the neutron stars, except for n ~ 2n0 when the opening of the URCA processes takes place. We finally obtain the thermal conductivity from phonon collisions and compare it with the electron thermal conductivity in superfluid neutron stars.
Speaker: Dr Laura Tolos (ICE (CSIC-IEEC))
• 15:10
Tests of the nuclear equation of state and superfluid and superconducting gaps using the Cassiopeia A neutron star 20m
The observed rapid cooling of the Cassiopeia A neutron star can be interpreted as being caused by neutron and proton transitions from normal to superfluid/superconducting states in the stellar core. Here we present measurements of the neutron star mass and radius found from consistent fitting of both the Chandra X-ray spectra and cooling behavior; this comparison is only possible for individual nuclear equations of state. We also test phenomenological superfluid and superconducting gap models, that mimic most of the known theoretical models, against the cooling behavior and obtain constraints on the gaps.
Speaker: Wynn Ho (U)
• 15:30
The neutron star in Cassiopeia A: equation of state, superfluidity, and Joule heating 20m
The thermomagnetic evolution of the young neutron star in Cassiopea A is studied by considering fast neutrino emission processes. In particular, we consider neutron star models obtained from the equation of state computed in the framework of the Brueckner-Bethe-Goldstone many-body theory and variational methods, and models obtained with the Akmal-Pandharipande-Ravenhall equation of state. It is shown that it is possible to explain a fast cooling regime as the one observed in the neutron star in Cassiopea A if the Joule heating produced by dissipation of the small-scale magnetic field in the crust is taken into account. We thus argue that it is difficult to put severe constraints on the superfluid gap if the Joule heating is considered.
Speaker: Dr Alfio Bonanno (INAF-Catania)
• 15:50
Effects of superfluidity on cooling of compact stars 20m
I will discuss the recent work on the effects of superfluidity of baryonic and quark matter on the cooling of compact stars. In particular I will focus on the effects of (1) pair-breaking processes on the cooling; (2) color superconductivity; and (3) the problem of the fitting of Cas A data with different models.
Speaker: Armen Sedrakian (Frankfurt University)
• 16:10
Thermal Evolution of Compact Stars with Color Superconducting Quark Matter 20m
The observations of the central source of Cassiopeia A (Cas A) indicates that the compact star has large mass and high effective temperature, and suggests that its location on the cooling diagram is in the standard cooling region. There are some other compact stars which have low effective temperature, and they require an exotic phase which appears at high density, for large neutrino emissivity. Assuming the cooled stars have larger mass than the mass of Cas A, it seems to satisfy the temperature observations, but they should have very large masses. It may conflict with the mass observation of other compact stars in binary systems. We investigate the effect of the color superconducting quark matter phase on the thermal evolution of compact stars. We assume the color superconducting quark phase has large energy gap, and we simulate the thermal evolution of the compact stars. We present cooling curves obtained from the evolutionary calculations of compact stars: while heavier stars cool slowly, and lighter ones indicate the opposite tendency.
Speaker: Dr Tsuneo Noda (Kurume Institute of Technology)
• 14:30 16:30
Afternoon session - Parallel B
Convener: Alice Harding (NASA, USA)
• 14:30
Origin and evolution of magnetars 20m
Up to now it is unclear how magnetars obtain their large magnetic fields. In the standard model it is proposed that fields are enhanced via a dynamo mechanism. This scenario requires that the neutron star has very rapid initial rotation. Such assumption, on one hand, requires rapid rotation of the progenitor, and so a specific evolution; on another hand, this assumption leads us to potentially testable predictions. At first we study evolutionary channels in binary evolution which can produce rapidly rotating massive stellar cores prior to collapse. It is demonstrated that in an optimistic scenario one can easily explain the fraction of magnetars among all NSs and the fact that all known sources of this kind are isolated. In a very conservative approach the fraction of magnetars is also reproduced, but it is necessary to assume correlation between initial spin and kick velocity to explain the absence of companions for known magnetars. Then we study evolution of magnetars in close binary systems, and demonstrate that the observational data is in correspondence with the standard magnetic field decay scenario. Finally, we discuss the possibility that some of CCOs are magnetars which experienced very strong fall-back, in particular we look at the case of Kes 79 where a NS has relatively long spin period (in comparison with what is necessary for effective dynamo). A discovery of an anti-magnetar with a millisecond period and strong crustal field identifiable, for example, due to large pulse fraction, would be the proof of the dynamo field origin. Existence of such sources is in correspondence with the present standard picture of neutron star unification. However, the fraction of magnetars with submerged fields can be small --- few percent of the total number of CCOs.
Speaker: Dr Sergei Popov (SAI Moscow)
• 14:50
Partially Screened Gap in Pulsars 20m
Coherent pulsar radio emission requires an existence of inner acceleration region above the polar cap. The most advanced implementation of the inner gap idea is the Partially Screened Gap (PSG) model, based on recent calculations of the surface binding energy and Hall drift induced surface magnetic field in neutron stars. The PSG model has a great predictive power and can be tested observationally both in radio band and X-rays. PSR B0943+10, which was extensively observed and studied in both these bands, is an ideal testing case. We demonstrate that all the observational characteristics of PSR B0943+10 are fully consitent with the PSG pulsar model. This has important consequences for understanding the physics of pulsar radio emission mechanism.
Speaker: Dr Andrzej Szary (Kepler Institute of Astronomy, Univ. Zielona Gora, Poland)
• 15:10
Clues to the formation and evolution of magnetars from X-ray observations of the associated supernova remnants 20m
Magnetars, i.e., neutron stars (NSs) with extremely strong magnetic fields, are thought to be produced by Type II supernovae (SNe), like other NSs. Indeed, several of them are located inside supernova remnants (SNRs). However, we do not know how the magnetar-producing SNe differ from those creating the other NSs. Observations of the SNRs associated with magnetars are expected to provide key information on the above issue. Using Suzaku, the 5th Japanese X-ray satellite, we observed the SNR CTB109 hosting the magnetar (AXP) 1E 2259+586. From measured temperatures of the X-ray emitting plasmas, we estimated the SNR age as 13 kyr, and the explosion energy as 0.7e+51 erg, both in agreement with previous estimates (e.g. Sasaki et al. 2012). These and other X-ray properties of CTB109, including its abundance patterns, were not significantly different from those of other Type II SNRs. However, we reconfirmed the huge discrepancy between the age (1.3 kyr) of CTB109 estimated in this way and the measured characteristic age of 1E 2259+586, 230 ky. We presume that this age problem arises because characteristic ages of pulsars (including magnetars) are generally calculated assuming constant fields, whereas magnetars must be spending its magnetic energy and hence their magnetic fields must be decaying with time. Employing a simple power-law decay of the magnetic field (e.g., Colpi et al. 2000, Dall'Osso et al. 2012), we successfully obtained a family of field-decay solutions that can explain away the age discrepancy between CTB109 and its magnetar. This result has several important implications. First, the apparent age overestimations of magnetars are now considered, conversely, to provide evidence for the magnetically-powered nature of magnetars. Second, it directly follows that magnetars are likely to be systematically younger than previously thought. This view is further supported by a systematic difference between magnetars and pulsars in their Galactic spatial distributions. Finally, the magnetar birth rate must be accordingly much higher than considered before, and hence a considerably fraction of Type II SNe may produce magnetars rather than ordinary pulsars with ~1e12 G magnetic fields.
Speaker: Toshio Nakano (University of tokyo)
• 15:30
Effect of strong magnetic ﬁelds on the nuclear “pasta” phase structure 15m
The effect of strong magnetic ﬁelds on the properties of the pasta structure is calculated within a Thomas-Fermi approach using relativistic mean-ﬁeld models to modulate stellar matter. It is shown how quantities such as the size of the clusters and Wigner-Seitz cells, the surface tension, and the transition between conﬁgurations are affected. It is expected that these effects may give rise to large stresses in the pasta phase if the local magnetic ﬁeld suffers ﬂuctuations.
Speaker: Dr Rafael C. R. de Lima (Universidade do Estado de Santa Catarina)
• 15:45
Stellar compact objects under strong magnetic fields 15m
We apply magnetic fields of the order of 10^17 G and 10^18 G to nuclear matter, and study its influence on the symmetry energy and its slope. We also study the effects caused by the inclusion of anomalous magnetic moments to these quantities. Then, we investigate the effects caused by strong magnetic fields on the properties of compact objects, composed by hadronic matter in β-equilibrium, interacting via (σ − ω − ρ) mesonic fields. To do so we use the non-linear Walecka model and some parametrizations normally found in the literature. Submitting hadronic matter to magnetic fields of the order of 10^17 G and 10^18 G, we also study the effects of the inclusion of the anomalous magnetic moment to the equations of state and corresponding mass-radius relation. We also study the effects of the inclusion of a term that takes into account the interaction between the ω and ρ mesons subject to strong magnetic fields. At last we compare the obtained curves for the theoretical models with three known binary systems observation data.
Speaker: Dr Rudiney Casali (Institut de Physique Nucléaire de Lyon)
• 16:00
What makes magnetars (as well as normal pulsars) radio laud? 15m
We present circumstances that should be fulfilled in the magnetosphere of the neutron stars to “switch” the mechanism for radio emission on. We claim that the curvature of magnetic field lines at the stellar surface is the most influential factor affecting the radio emission process. The most plausible mechanism for the radio emission which most probably is the coherent curvature radiation requires creation of a secondary plasma with the proper parameters (density, Lorentz factor etc.). Such a plasma can be only created if the curvature radius of the surface magnetic field lines is significantly less than 10^8 cm which is a canonical value for the purely dipole magnetic field. Corresponding scenarios that cause the significant increase of the curvature in pair creation regions for magnetars and pulsars differ very much. Then further in the radio emission region, the plasma instabilities lead to the coherent curvature radiation. We discuss possible processes that can affect the curvature and present observational evidences that support our model.
Speaker: Prof. George Melikidze (J. Kepler Institute of Astronomy, University of Zielona Gora, Poland)
• 16:15
Azimuthally-structured radio beams of pulsars 15m
There is a growing evidence that radio beams of some pulsars are azimuthally-structured. When viewed down the dipole axis, the beam resembles spokes in a wheel, with narrow emission stripes spreading away from the dipole axis. I will present objects for which the spoke-like model describes their profiles more successfully than the traditional conal geometry. Further from the dipole axis, the stripes do not widen as would be expected for a structure limited by lines of fixed magnetic azimuth. Hence the mathematical formulae that describe the beam do not result from a simple projection of dipolar field lines on the sky. With the ambiguity of pulsar geometry determination through the gamma-ray- or polarisation-based methods, the task is hindered by the unknown radio beam geometry, and the conal interpretation of profiles can be misleading.
Speaker: Dr Jaroslaw Dyks (Nicolaus Copernicus Astronomical Center)
• 16:30 17:00
Coffee break 30m
• 17:00 18:30
Evening session - Parallel A
Convener: Nicolas Chamel (Universitè Libre de Bruxelles, Belgium)
• 17:00
Sound modes and instabilities in a relativistic superfluid 20m
Compact stars are likely to contain superfluid matter, either in the form of nuclear or quark matter, or both. The hydrodynamics of superfluids is usually described in terms of a two-fluid model. I will discuss how such a two-fluid model can be derived from field theory and apply the results to compute the properties of first and second sound for arbitrary temperatures and (uniform) superfluid velocities. I will also discuss the two-stream instability - known from plasma physics - that manifests itself in an unstable sound mode and that is potentially relevant for the fluid dynamics in the interior of the star.
Speaker: Andreas Schmitt (Vienna University of Technology)
• 17:20
Effects of the symmetry energy in core-collapse supernovae 20m
This presentation discusses the role of the equation of state (EOS) in core-collapse supernovae, with focus on the nuclear symmetry energy. First we review the extended set of supernova EOS which we have developed recently and compare their characteristic properties with experimental constraints. The new EOSs are then applied in hydrodynamical simulations with detailed neutrino transport, where we investigate effects on the supernova dynamics and implications on nucleosynthesis conditions in the so-called wind phase. Regarding the latter, we can conclude that the current constraints on the finite-temperature symmetry energy allow only slightly neutron-rich conditions which would not result in a full r-process.
Speaker: Matthias Hempel (B)
• 17:40
The equation of state from chiral forces in the Green's functions approach 20m
The equation of state of neutron matter is a basic ingredient in the theoretical understanding of neutron stars. From a nuclear theory perspective, the problem has two major sources of uncertainty: the nuclear hamiltonian and the treatment of quantum many-body correlations. I will review a series of recent theoretical advances within the many-body Green's functions approach that help tackle both sources. First, I will discuss how chiral effective field theory two-body forces can be incorporated into the Green's functions approach, to obtain single-particle and bulk properties [1]. Chiral forces represent a step forward in having a direct connection to QCD and a quantifiable uncertainty. Second, I will introduce a new diagrammatic approach to include three-body forces consistently in the many-body formalism [2]. This improves saturation properties, but also the available equation of state [3]. The errors coming from many-body theory can be obtained by looking at different many-body approaches. Finally, I will mention potential future improvements to both chiral theory and many-body techniques. [1] A. Rios, A. Polls and W. H. Dickhoff, arXiv:1312.7307. [2] A. Carbone, A. Cipollone, C. Barbieri, A. Rios and A. Polls, Phys. Rev. C 88, 054326 (2013). [3] A. Carbone, A. Polls and A. Rios, Phys. Rev. C 88, 044302 (2013).
Speaker: Dr Arnau Rios Huguet (University of Surrey)
• 18:00
Numerical studies of the dynamical bar-mode instability in rapidly rotating relativistic stars 15m
We present numerical results on the dynamical bar-mode (m=2) instability in differentially rotating relativistic star models with a polytropic EoS, obtained by means of full 3D ideal magneto-hydrodynamics simulations in full General Relativity. We focus our attention on two different ingredients that may affect the onset and the dynamics of the instability, i.e., the magnetization and the stiffness of the EoS. The first study is carried out by superimposing to initial (matter) equilibrium configurations purely poloidal magnetic fields of different strength (in the range $10^{12}$-$10^{16}$ Gauss). We find that magnetic fields of order $10^{15}$ Gauss or less have negligible effects on bar-mode unstable models, while stronger magnetic fields are able to completely suppress the hydrodynamic instability which is present in the unmagnetized case. The second study is carried out by changing the adiabatic index of the polytropic EoS from 2 to 2.75, in order to mimic the behavior of a realistic EoS. We determine the change on the threshold for the emergence of the instability. We also extend the analysis to low values of the instability parameter \beta to check for the presence of low-\beta or shear instabilities.
Speaker: Dr Luca Franci (Università di Parma)
• 18:15
Neutron star metamorphosis: from sub-luminous accretion to rotation-powered quiescence 15m
The X-ray transient IGR J18245-2452 contains the first neutron star (NS) seen to switch between rotation-powered and accretion-powered pulsations. We present Swift and Chandra observations that reveal a spectral transition when the X-ray luminosity was as low as 0.01% of the Eddington limit. We also find a striking variability pattern in the 2008 quiescent Chandra light curves: rapid switches between a high-luminosity active' state and a low-luminosity passive' state, with no detectable spectral change. We discuss these results in the context of slowly accreting compact objects and millisecond radio pulsars, and propose a scenario where the observed mode switches in quiescence are caused by fast transitions between the magnetospheric accretion and pulsar wind shock emission regimes.
Speaker: Manuel Linares (I)
• 17:00 18:30
Evening session - Parallel B
Convener: Jerome Margueron (IPN Lyon, France)
• 17:00
Symmetry energy and neutron star radii 15m
We introduce two sets of models with symmetry energy functionals which at high baryon densities differ in stiffness. The symmetric part of the energy per baryon is the same for all models and is based on the APR EoS. We test the behavior of the symmetry energy by using a constraint on the total baryon mass for a gravitational mass of a 1.25 M$_{\odot}$ neutron star. This constraint is the result of an study perfomed by Kitaura et al. on stellar explosions of stars with an O-Ne_Mg core. Since the symmetry energy is closely related to the proton fraction of neutron star matter, we discuss the role of the DUrca cooling since it can be activated above some threshold on the proton content. We conclude with showing the favored models and their corresponding effects on the neutron star radius.
Speaker: David Blaschke (University of Wroclaw)
• 17:30
Nucleon effective masses within the Brueckner-Hartree-Fock theory: Impact on stellar neutrino emission 15m
We calculate the effective masses of neutrons and protons in dense nuclear matter within the microscopic Brueckner-Hartree-Fock many-body theory and study the impact on the neutrino emissivity processes of neu- tron stars. We compare results based on different nucleon-nucleon potentials and nuclear three-body forces. Useful parametrizations of the numerical results are given. We find substantial in-medium suppression of the emissivities, strongly dependent on the interactions.
Speaker: Mr Gabriele Taranto (INFN)
• 17:45
Properties of Infinite Nuclear Matter and Neutron Star Matter with the Gogny Interaction 15m
The equation of state and internal composition of neutron stars is not very well constrained yet. In this work, I have used theoretical nuclear physics techniques to predict the bulk properties of neutron stars starting from the Gogny interaction. The results of 10 different parametrizations of this nuclear interaction have been compared to constraints obtained from nuclear physics experiments. Only 1 interaction falls within the available window. I will further compare neutron star properties to astronomical observations and describe how to improve these interactions for dense matter physics.
Speaker: Mr Roshan Sellahewa (University of Surrey)
• 18:00
PROPERTIES OF LOCALIZED PROTONS IN NEUTRON STAR MATTER AT FINITE TEMPERATURES 15m
We study properties of the proton component of neutron star matter for a number of realistic nuclear models. Vanishing of the nuclear symmetry energy implies proton-neutron separation in dense nuclear matter. Protons which form admixture tend to be localized in potential wells. Here we extend the description of proton localization to finite temperatures. It appears that the protons are still localized at temperatures typical for hot neutron stars. That fact has important astrophysical consequences. Moreover, the temperature inclusion leads to unexpected results for the behaviour of the proton localized state.
Speaker: Dr Adam Szmagliński (Institute of Physics, Cracow University of Technology)
• 18:15
Quark-Model Baryon-Baryon Interaction and Its Prospects in the Nuclear Matter Physics 15m
Baryon-baryon (BB) interactions are most fundamental in nuclear structure and matter properties. The purpose of this talk is to discuss properties of the realistic quark-model (QM) BB interaction and the prospects in the application to the nuclear matter physics. QM BB interactions are constructed in the framework of resonating-group method for two three-quark clusters[1]. QM BB interactions have two interesting features. One is the nucleon-nucleon (NN) short-range repulsion described by the nonlocal quark-exchange kernel, which gives quite different off-shell properties from standard meson-exchange potentials. The other is the Pauli principle on the quark level, which makes the ΣN (I=1/2) channel repulsive. The most developed version of the QM by Kyoto-Niigata group, fss2, has achieved accurate descriptions of available NN and Y N experimental data[2]. It has been successfully applied to the three-baryon systems (3H, 3ΛH[3] and three-nucleon scattering[4]) using the Faddeev frame- work. We now aim to apply the QM fss2 to the Brueckner-Hartree-Fock calculation. In this presentation, we introduce the general properties of the QM BB interactions and would like to discuss the prospects in the applications to the nuclear matter. 1. M. Oka, K. Yazaki, Phys. Lett. 90B, 41 (1980), Prog. Theor. Phys. 66, 556, 572 (1981). 2. Y. Fujiwara, Y. Suzuki and C. Nakamoto, Prog. Part. Nucl. Phys. 58, 439 (2007). 3. Y. Fujiwara, Y. Suzuki, M. Kohno and K. Miyagawa, Phys. Rev. C77, 027001 (2008). 4. Y. Fujiwara and K. Fukukawa, Few-Body Syst. 54, 2357 (2013), and references therein.
Speaker: Dr Kenji Fukukawa (INFN Sezione di Catania)
• Wednesday, 26 March
• 09:00 11:00
Plenary session 5
Convener: Nils Andersson (Universitty of Southampton)
• 09:00
The extreme activity of strong and low magnetic magnetars 40m
I will review the latest observational results on strongly magnetized neutron stars, underlying the evolutionary connection of these objects with the rest of the isolated pulsar population. In this respect, I will show how the recent discovery of three low magnetic field magnetars was crucial in understanding the evolutionary link between different isolated neutron star classes.
Speaker: Dr Nanda Rea (nstitute of Space Sciences (CSIC-IEEC), Barcelona, ES)
• 09:40
Towards the great unification of neutron stars 40m
Observations of magnetars and some of the high magnetic field pulsars have shown that their thermal luminosity is systematically higher than that of classical radio-pulsars, thus confirming the idea that magnetic fields are involved in their X-ray emission. In this talk I review the most recent results of 2D simulations of the fully coupled evolution of temperature and magnetic field in neutron stars, including the state-of-the-art kinetic coefficients and, for the first time, the important effect of the Hall term. After analysing all the best available data on isolated, thermally emitting neutron stars (a data sample of 40 sources), we discuss which evolutionary models can explain the phenomenological diversity of magnetars, high-B radio-pulsars, and isolated nearby neutron stars by only varying their initial magnetic field, mass and envelope composition. Nearly all sources appear to follow the expectations of the standard theoretical models. Finally, we discuss the expected outburst rates and the evolutionary links between different classes. This results constitute a major step towards the grand unification of the isolated neutron star zoo.
Speaker: Prof. Jose Pons (University of Alicante, Spain)
• 10:20
Magnetic energy dissipation and emission from magnetars 40m
Mechanisms of energy dissipation in magnetars will be discussed, including dissipation inside and outside the neutron star. Different modes of dissipation are responsible for various components of magnetar activity: persistent emission and bursts, thermal and nonthermal X-ray emission, and low-frequency emission.
Speaker: Dr Andrei Beloborodov (Columbia University)
• 11:00 11:30
Coffee break 30m
• 11:30 12:50
Plenary session 6
Convener: Nils Andersson (Universitty of Southampton)
• 11:30
The connection between core-collapse supernovae and Gamma-Ray Bursts 40m
A few long Gamma-Ray Bursts and X-ray Flashes at redshift lower than ~0.3 are firmly associated with well studied core-collapse stripped-envelope Supernovae with broad spectral lines and high kinetic energies. A number of higher redshift GRBs are also accompanied by Supernovae that have properties consistent with those of energetic core-collapse SNe. This suggests that the majority of long GRBs are generated by Supernovae. However, the exceptions compound this picture and suggest different evolutionary pathways and endpoints for the GRB progenitors.
Speaker: Dr Elena Pian (INAF, Italy)
• 12:10
GRB central engines 40m
The character of the prompt emission, of the afterglow, the presence of an associated supernova (SN), and the environment, all characterize and constrain the possible central engine of Long and Short Gamma Ray Bursts (GRBs). However, despite the observed variety, there is little diversity among models for the central engine and essentially all can be simply classified as a rotating compact object that drives an asymmetric relativistic outflow. The two leading models are the “collapsar” and the “millisecond proto-magnetar.” I will briefly review the various criteria that any model must satisfy, and I will illustrate the key ideas behind both the collapsar and millisecond magnetar, with their strengths and weakness, especially in the light of the recent observation of the so called "late activity".
Speaker: Dr Niccolò Bucciantini (INAF Osservatorio di Arcetri)
• 12:50 14:30
Lunch break 1h 40m
• 14:30 15:10
Plenary session 7
Convener: Nils Andersson (Universitty of Southampton)
• 14:30
Data sets of equation of state for core-collapse supernovae: their impact on dynamics and signals 40m
Properties of hot and dense matter play a key role in the explosion dynamics of core-collapse supernovae. The equation of state (EOS) affects the energetics of core-bounce and the following revival of shock wave for explosions. The EOS determines the final fate of compact objects together with emergent signals of neutrinos. Therefore, systematic sets of data for supernova EOS are essential ingredients in numerical simulations of supernovae. In this presentation, I review critical and delicate roles of EOS in the supernova dynamics, the birth of compact objects and the associated signals. I would like to stress efforts on constructing sets of supernova EOS to cover the extreme and variable conditions in supernova cores beyond neutron star EOSs. I illustrate the importance of systematic descriptions of nuclear matter, composition and associated neutrino reactions as wells as systematic explorations of EOS effects in multi-dimensional simulations for the successful explosion.
Speaker: Prof. Kohsuke Sumiyoshi (Numazu College of Technology, Japan)
• 15:15 16:30
Afternoon session - Parallel A
Convener: Jorge Horvath (IAG-USP)
• 15:15
The effects of a neutron star translational and rotational motion in observable timing and evolution of radiopulsars 20m
The instant observed period of an isolated radiopulsar is accepted to be identical to the physical period of a neutron star rotation except for the cases of obvious strong precession. However, in the strict sense, the time interval between two successive pulses received by an observer is nothing else than the interval between successive passes of the observer through rotating pulsar beam. And this interval is not necessarily equal to the current physical period of the neutron star. Since the star is affected by an electromagnetic braking torque and is not spherical, it is liable to forced and free precessions that result in the complex rotation of pulsar beam relative to the observer. Thus the observed pulsar period becomes a slightly different from the physical one. In our work we derive analytically and analyse corresponding "geometric" contribution to time evolution of the observed pulsar period. We show that for NS with typical parameters, even non-spherical ones, this contribution does not affect pulsar observables significantly. Instead, a slowly precessing neutron star looks like a non-precessing one with a period which systematically (and slightly) differs from a physical period of NS rotation. Thus, in particular, the nature of anomalous values of pulsars braking indices can not be merely geometrical. If NS complex rotation is indeed the trigger of braking indices high values, then one needs to postulate an existence of a some mediator mechanism. We also derive and analyse effects of a translation motion of a NS. The observer gradually leaves pulsar beam due to systematic change of an angle between NS radius vector and spin axis caused by NS motion. We show that the timescale of this process is significantly less than typical pulsar lifetime. On the other hand, the same effect also causes the appearance of "new" kindling pulsars in the observed subset due to the observer's entrance into the beam of an initially "hidden" pulsar. And the rate of the latter process seems to be higher than the one of a pulsars physical birth. We conclude that both effects should have strong selectional impact on the observed pulsars subset.
Speaker: Anton Biryukov
• 15:35
The glitch activity of the Crab pulsar 20m
The rotation of the Crab pulsar has been regularly monitored at Jodrell Bank Observatory and other observatories for 44 years. Like most pulsars, its regular spindown is occasionally interrupted by sudden spin-up events known as glitches. Glitches are thought to be the response of a dense internal neutron superfluid to the pulsar's spindown. Here we report on a detailed study of the rotation stability of the Crab pulsar. We identify all the glitches and find that their sizes are well above the detectability limits, allowing us to uncover the full size distribution. The distribution falls off as glitch size decreases and indicates the existence of a minimum size, thereby challenging the predictions of most glitch models. In addition to the glitches, we also identify a low-amplitud separate population of irregularities that present clear noise properties. Glitches can greatly affect the long-term spin evolution of pulsars and for the Crab pulsar the main disturbance is the one caused by persistent step-changes in spindown rate occurring at every glitch. We find that these steps reverse the general spindown trend by ~5% and that their amplitudes are correlated with the size of the glitches. In addition, the time series of the glitches exhibits a 10-year period of increased activity which introduces further, unexpected effects on the rotational behaviour.
Speaker: Cristobal Espinoza (P)
• 15:55
Nuclear equation of state from observations of short gamma-ray burst remnants 20m
The favoured progenitor model for short gamma-ray bursts (SGRBs) is the merger of two neutron stars that triggers an explosion with a burst of collimated gamma-rays. Following the initial prompt emission, some SGRBs exhibit a plateau phase in their X-ray light curves that indicates additional energy injection from a central engine, believed to be a rapidly rotating, highly magnetised neutron star. The collapse of this protomagnetar' to a black hole is likely to be responsible for a steep decay in X-ray flux observed at the end of the plateau. I will show how these observations can be used to effectively constrain the equation of state of dense matter. In particular, I will show that the known distribution of masses in binary neutron star systems, together with fits to the X-ray light curves, provide constraints that exclude the softest and stiffest plausible equations of state. I further illustrate how a future gravitational wave observation with Advanced LIGO/Virgo can place tight constraints on the equation of state, by adding into the picture a measurement of the chirp mass of the SGRB progenitor.
Speaker: Dr Paul Lasky (School of Physics, melbourne University)
• 16:15
GRB 130831A: The Birth and Death of a Magnetar at z=0.5 15m
We present observations of GRB 130831A obtained by Swift, Chandra, and multiple ground-based observatories. This burst shows a remarkable drop in the X-ray light curve at about 10^5 s after the trigger, with a decay slope of \alpha_X \simeq 5. Such behaviour cannot be explained in the standard Forward Shock (FS) model, whereas it can be explained if the high energy emission is powered by a newly born magnetar. After the drop, the X-ray afterglow resumes a decay with a slope more typical of FS emission. The optical emission, on the other hand, shows no clear break across the X-ray drop, and its decay is similar to that of the late X-rays. We assume that the optical and late X-ray emission are both FS; we model our data to derive the kinetic energy of the ejecta and thus measure, for the first time, the efficiency of the magnetar as central engine of a Gamma-Ray Burst.
Speaker: Dr M. De Pasquale (Mullard Space Science Laboratory - University College London)
• 15:15 16:30
Afternoon session - Parallel B
Convener: Francesca Gulminelli (LPC Caen, France)
• 15:15
Neutron stars and nuclear matter parameters 20m
Neutron stars can be suitable laboratory to see the physics under the ultra-high density region. The direct observations of neutron stars help us to understand the nuclear matter properties and equation of state. On the other hand, the terrestrial nuclear experiments directly reveal such properties especially around the saturation density, which are strongly coupled with not only the crust region in the neutron stars but also the stellar structure of low-mass neutron stars. In this talk, we show the possibility to derive the nuclear properties from the astrophysical observational point of view. In particular, we focus on the nuclear symmetry energy, adopting the observation of quasi-periodic oscillations of giant flares in soft-gamma repeaters. In addition to showing of our results, we will discuss the additional effect to take into account in future.
Speaker: Hajime SOTANI (Kyoto University)
• 15:35
Obtaining the neutron star gravitational mass limit in the frame work of the LOCV method 20m
Using the lowest order constrained variational method (LOCV) we calculate the equation of state of pure neutron matter (PNM) as well as the charge neutral (n,p,e,μ) matter in beta equilibrium with AV18 two-body nucleon-nucleon interaction supplemented by a microscopic three-body force. The neutron star gravitational mass limit obtained with this interaction is 2.62 M⊙ for PNM and 2.41 M⊙ in case of the beta stable matter. The effects of the three-body force on the gravitational mass limit of the neutron stars are also discussed and the results are compared with the others many-body calculations.
Speaker: Hamidreza Moshfegh (University of Tehran)
• 15:55
Electromagnetic signals from bare strange stars 20m
Strange stars with a crystalline color superconducting crust can sustain large shear stresses, supporting torsional oscillations of large amplitude. Moreover if a bare quark matter surface is present electrons spill in the star exterior forming an electromagnetically bounded atmosphere hundreds of Fermi thick. We investigate the electromagnetic signature connected with a torsional oscillation of the crust. The emitted power could be of the order of 10^51 erg/s. The emission is in the radio frequency band with estimated relaxation times ranging between milliseconds, for a 1 km thick crust, to minutes, for a 9 km crust.
Speaker: Dr Giulia Pagliaroli (INFN - LNGS)
• 16:15
Inhomogeneous structures of neutron star crust and mechanical properties 15m
We investigate inhomogeneous structures and properties of low-density nuclear matter by a relativistic mean-field approach with a fully three-dimensional geometry [1]. By avoiding usage of Wigner-Seitz approximation, we can discuss a priori the structure of matter. We show that nuclear droplets form a body-centered-cubic (bcc) lattice at lower densities. With increasing density, it changes to a face-centered-cubic (fcc) lattice before nuclear shapes change from spherical droplets to cylindrical rods [2]. The conventional studies predict only the appearance of bcc lattice which minimizes the Coulomb energy. On the other hand, our calculation indicates that the change of the size and shape of droplet affects the lattice structure. As an application of our new framework, we calculate some parameters of mechanical strength of matter, such as shear modulus.　Here, we do not use any simplification but directly obtain the curvature of the energy versus shear deformation. We compare our results with that of analytic calculation. [1] M. Okamoto, et al, Phys. Lett. B 713, 284 (2012) [2] M. Okamoto, et al, Phys. Rev. C 88, 025801 (2013)
Speaker: Toshiki Maruyama (Japan Atomic Energy Agency)
• 16:30 17:00
Coffee break 30m
• 17:00 18:40
Evening session - Parallel A
Convener: H.-Thomas Janka (MPI Garching, Germany)
• 17:00
The long-term post-outburst spin down of low magnetic field magnetar Swift J1822.3-1606 20m
The magnetar Swift J1822.3-1606 was discovered when it entered an outburst phase in 2011 July. Previous X-ray studies of its post-outburst rotational evolution yielded inconsistent measurements of the spin-inferred magnetic field. However, it was clear that Swift J1822.3-1606 has the second lowest spin-inferred magnetic field of all known magnetars. Here we present the timing behavior and flux relaxation from over two years of Swift, RXTE, and Chandra observations following the outburst. We find that the ambiguity in previous timing solutions was due to enhanced spin down that resembles an exponential recovery following a glitch at the outburst onset. After fitting out the effects of the recovery, we measure a long-term spin-down rate which implies a dipolar magnetic field that is lower than all previous estimates for this source. We also consider the post-outburst flux evolution, and fit it with both empirical and crustal cooling models. We discuss the flux relaxation in the context of both crustal cooling and magnetospheric relaxation models.
Speaker: Mr Paul Scholz (McGill University)
• 17:20
Repeated, Delayed Torque Instabilities Following Flux Enhancement in the Magnetar 1E 1048.1 5937 20m
1E 1048.1-5937 is one of the most active magnetars, having exhibited three long-term flux flares, as well as several SGR-like bursts, pulse profile changes, and timing anomalies in 16 years of previous monitoring. This pulsar has also displayed behavior not seen in any other magnetar: on the order of 100 days after the start of two of these flux flares, the spin-down rate underwent a period of greatly increased variability for the approximately two years. These bizarre episodes, in which the spin-down rate changed abruptly by a factor of as much as 10, are a significant puzzle in magnetar astrophysics and, if repeatable, suggest the slow build-up of outer magnetospheric twisting as suggested by Beloborodov (2009) . Here we report a fourth flux flare in 1E 1048.1-5937 as observed in X-ray timing observations obtained using the Swift X-ray Telescope in December 2011. We show that again roughly 100 days following the flare, the pulsar's spin-down rate began showing large variations, with the source presently being in this state. This strongly suggests that such flare/torque change delays are repeatable in this source. Why such delayed spin-down variations are seen thus far uniquely in 1E 1048.1-5937 remains puzzling.
Speaker: Robert Archibald
• 17:40
Superfluid magneto-elastic oscillations in Magnetars 20m
Our numerical simulations show that axisymmetric, torsional, magnetoelastic oscillations of magnetars with a superfluid core can explain the whole range of observed quasiperiodic oscillations (QPOs) in the giant flares of soft gamma-ray repeaters. There exist constant phase QPOs at $f\lesssim150$\,Hz and resonantly excited high-frequency QPOs ($f>500$\,Hz), in good agreement with observations. The range of magnetic field strengths required to match the observed QPO frequencies agrees with that from spin-down estimates. These results suggest that there is at least one superfluid species in magnetar cores.
Speaker: Dr Michael Gabler (MPA Garching)
• 18:00
Superfluid and superconducting magnetars and QPO spectrum 20m
The analysis of Quasi Periodic Oscillations (QPOs) in Magnetars provided the first application of Asteroseismology in neutron stars. These oscillations are likely identified with magneto-elastic waves which originate in the giant flares. Cooling calculations show that magnetars become superfluid/superconducting systems in few hundred years from their birth. In this talk I will present the first dynamical study of superfluid magnetar models which incorporate the physics of superconducting protons and show its implications for the QPO Asteroseismology.
Speaker: Dr Andrea Passamonti (INAF-Observatory of Rome)
• 18:20
Three evolutionary paths for magnetar oscillations 20m
Quasi-periodic oscillations have been seen in the light curves following several magnetar giant flares. These oscillations are of great interest as they probably provide our first ever view of the normal modes of oscillation of neutron stars. The state-of-the-art lies in the study of the oscillations of elastic-magnetic stellar models, mainly with a view to relating the observed frequencies to the structure and composition of the star itself. We advance this programme by considering several new physical mechanisms that are likely to be important for magnetar oscillations. These relate to the superfluid/superconducting nature of the stellar interior, and the damping of the modes, both through internal dissipation mechanisms and the launching of waves into the magnetosphere. We make simple order-of-magnitude estimates to show that both the frequencies and the damping time of magnetar oscillations can evolve in time, identifying three distinct pathways' that can be followed, depending upon the initial magnitude of the mode excitation. These results are interesting as they show that the information buried in magnetar QPOs may be even richer than previously thought, and motivate more careful examination of magnetar light curves, to search for signatures of the different types of evolution that we have identified.
Speaker: Kostas Glampedakis
• 17:00 18:15
Evening session - Parallel B
Convener: Juergen Schaffner-Bielich (Frankfurt University)
• 17:00
Equation of State for Neutron Stars based on a microscopic energy density functional : from the outer crust to the core 20m
Within a microscopic approximation the structure of Neutron Stars is usually studied by modelling the homogeneous nuclear matter of the core by a suitable Equation of State, based on a many-body theory, and the crust by a functional based on a more phenomenological approach. We present here the first calculation of Neutron Star overall structure by adopting for the core an Equation of State derived from the Brueckner-Hartree-Fock theory [1] and for the crust the so-called Barcelona-Catania-Paris-Madrid (BCPM) Energy Density Functional which is based on the same Equation of State, and which is able to provide accurately the binding energy of nuclei throughout the mass table [2]. The outer core is treated in the standard manner with the nuclear masses computed at the Hartree-Fock plus BCS level. The inner crust calculation is performed in the Wigner-Seitz approximation using the self-consistent Thomas-Fermi method, which is able to describe not only spherical droplets but also pasta configurations such as rods, slabs and spherical and cylindrical bubbles. Preliminary results about this new microscopic Equation of State have been reported in Ref. [3]. [1] M. Baldo, C. Maieron, P. Schuck and X. Vinas, Nucl. Phys. A736, 241 (2004). [2] M. Baldo, L. Robledo, P. Schuck and X. Vinas, Phys. Rev. C87, 064305 (2013). [3] M. Baldo, G. F. Burgio, M. Centelles, B. K. Sharma and X. Vin ̃as, arXiv 1308.2304, to be published in Phys. Atom. Nucl.
Speaker: Prof. Xavier Vinas (Universitat de Barcelona)
• 17:20
Unified equations of state of dense matter: nuclear-matter properties ….. 20m
A set of unified equations of state (EoSs) for neutron-star matter, based on generalised Skyrme energy-density functionals, will be presented. The underlying functionals will be discussed in connection with present data coming from nuclear physics experiments. The structure of neutron stars constructed with these EoSs will be discussed, in connection with both astrophysical observations (such as mass-radius relation and maximum mass) and nuclear-matter parameters (such as the symmetry energy).
Speaker: Dr Anthea Fantina (Institut d'Astronomie et d'Astrophysique, Université Libre de Bruxelles)
• 17:40
Nuclear pasta phase in core-collapse supernova matter 20m
The core-collapse supernova phenomenon, one of the most explosive events in the Universe, presents a challenge to theoretical astrophysics. Of the large variety of forms of matter present in core-collapse supernova, we focus on the transitional region between homogeneous (uniform) and inhomogeneous (pasta) phases. We perform a three-dimensional, finite temperature Skyrme-Hartree-Fock + BCS (3D-SHF) study of the inhomogeneous nuclear matter, where we calculate self-consistently the nuclear pasta phase and determine the phase transition between pasta and uniform matter. As the nuclear matter properties depend on the effective nucleon-nucleon interaction in the 3D-SHF model, we employ four different parametrizations of the Skyrme interaction, SkM∗, SLy4, NRAPR and SQMC700, and find subtle variations in the low density and high density transitions into and out of the pasta phase. One more stable pasta shape has been identified, in addition to the classic ones, on the grid of densities and temperatures used in this work. The data also indicate a discontinuity in the first derivatives of the free energy, which can be interpreted as a fingerprint of the first order transition between inhomogeneous and homogeneous supernova matter.
Speaker: Helena Pais (University of Coimbra)
• 18:00
Surface properties of nuclei embedded in a nucleon gas in the framework of the Extended Thomas-Fermi theory 15m
It is nowadays well established that the properties of the nuclear effective interaction through the equation of state have a very important influence in different astrophysical phenomena, from the dynamics of the Core Collapse Supernovae, to the cooling of Proto-Neutron Stars and the structure of Neutron Stars. The self-consistent mean-field theory is an appealing framework to establish a connection between astrophysical observations and fundamental properties of nuclear interactions. However the problem exists that the nuclear energy functional is still not sufficiently constrained in the isovector sector, inducing uncertainties in the modelization. In particular, it is very well known [1] that sub-saturation baryonic matter in such stars is organized as a Wigner-Seitz lattice of clusters embedded in a dilute nucleon gas. In the self-consistent mean-field theory, only the bulk properties of the cell can be analytically calculated from the basic isoscalar and isovector properties of the energy functional. A clear connection of the observables in star matter to the functional properties are thus not transparent. However, analytical expressions can be obtained in the framework of the Extended Thomas-Fermi (ETF) approximation [2, 3]. In this presentation, we discuss an ETF analytical model to describe the surface properties of such matter [4, 5]. More specifically, we derive analytical expressions for the density profile diffuseness and the corresponding surface energy for any cell, as a function of the underlying couplings of the energy functional. This model can be directly implemented in realistic finite temperature calculations of the stellar equation of state [6]. A special focus is given on the energetic modifications induced by the interaction between the cluster and the dilute medium, and a comparison to full HF calculations will be shown. ________________________________ [1] J. W. Negele and D. Vautherin, Nucl. Phys. A207, 298 (1973) [2] J. Treiner and H. Krivine, Annals of Phys. 170, 406 (1986) [3] H. Krivine and J. Treiner, Phys. Letters 124B (1983) [4] P. Papakonstantinou, J. Margueron, F. Gulminelli, and Ad.R. Raduta, Phys. Rev. C 82 045805 (2013) [5] Ad. R. Raduta, F. Aymard and F. Gulminelli, arXiv:1307.4202 [nucl-th] (to appear in EPJA) [6] Ad. R. Raduta and F. Gulminelli, Phys. Rev. C 82, 8065801 (2010)
Speaker: Mr François Aymard (LPC Caen, France)
• Thursday, 27 March
• 09:00 11:00
Plenary session 8
Convener: Ben Owen (Penn. State, USA)
• 09:00
Combustion processes in compact objects 40m
Compact objects can change their state and configuration in combustion processes. In the case of white dwarfs, thermonuclear burning leads to an explosion as Type Ia supernova -- a phenomenon well studied in observations and theoretical models. Combustion processes, however, may also be adequate to describe phase transitions in neutron stars, in particular the "burning" of hadronic matter into strange quark matter. I will discuss the physical concepts of combustion and describe methods to model this phenomenon in large-scale numerical simulations. These techniques are then applied to thermonuclear explosions of white dwarfs and to hypothetical "quark novae" transforming neutron stars into strange quark stars. While for Type Ia supernovae a wealth of observational data exists to validate these models, for quark novae only predictions for observables, such as neutrino signals, can be made.
Speaker: Prof. Friedrich Roepke (MPA Garching)
• 09:40
Gravitational Waves from Core-Collapse Supernovae 40m
The next galactic core-collapse supernova will be observed in the electromagnetic spectrum, in neutrinos, and, for the first time, in gravitational waves. I review gravitational wave emission from stellar collapse and the subsequent core-collapse supernova evolution and discuss how gravitational waves can be used to probe aspects of the explosion mechanism and physical parameters of the progenitor star.
Speaker: Dr Christian Ott (Caltech, USA)
• 10:20
Studying Pulsars with the Fermi Gamma-Ray Space Telescope 40m
Of the several thousand pulsars that have been discovered by radio telescopes over the past forty year, only a handful were known to emit gamma-ray pulsations before the launch in June, 2008 of the Fermi Gamma-Ray Space Telescope. After five years of operation, 130 gamma-ray pulsars have been detected and several new populations have been discovered. Millisecond pulsars have been confirmed as powerful sources of gamma-ray emission, and a whole population of these objects is seen with Fermi both in the Galactic plane and in globular clusters. Fermi has thus revolutionized the study of pulsars and allowed us to peer deeper into the inner workings of this incredibly efficient natural accelerator. These discoveries, together with recent progress in global simulation of pulsar magnetospheres, are changing our models of pulsar particle acceleration and high-energy emission.
Speaker: Prof. Alice K. Harding (NASA Goddard Space Flight Center)
• 11:00 11:30
Coffee break 30m
• 11:30 12:50
Plenary session 9
Convener: Ben Owen (Penn. State Univ., USA)
• 11:30
Probing the neutron star equation of state through X-ray spectroscopy 40m
Measurements of thermal radiation from neutron star surfaces offer the prospect of constraining the mass and radius of the neutron star. Such analyses require knowledge of how the atmosphere affect the radiation spectrum, the distance to the neutron star, and (for low energies) the effect of the interstellar medium. I will review methods using spectral lines, pulse profile modelling, X-ray burst spectral modelling, and quiescent LMXB spectral modelling, which can constrain the neutron star radius and/or the thermal properties of the neutron star (including the crustal conductivity and neutrino emission mechanisms).
Speaker: Craig Heinke (U)
• 12:10
Probing the neutron star equation of state through X-ray timing 40m
Modeling the amplitudes and shapes of the X-ray pulsations observed from hot, moderately or rapidly rotating neutron stars provides a direct method for measuring neutron-star properties. This method can in principle be applied to thermally emitting rotation-powered millisecond pulsars, millisecond oscillations from thermonuclear X-ray bursters, and accretion-powered millisecond pulsars, and it constitutes an important part of the science case for the forthcoming NICER and proposed LOFT X-ray missions. In this invited review, I will discuss the observables that can be derived from pulse profile modeling and show that analysis of pulse profiles from moderately spinning (300-800 Hz) pulsars in two different energy bands allows separate measurement of the neutron star mass and radius. I will also discuss the signal-to-noise levels required for measurements sufficient to constrain the neutron star equation of state.
Speaker: Deepto Chakrabarty (M)
• 12:50 14:30
Lunch break 1h 40m
• 14:30 15:45
Afternoon session - Parallel A
Convener: Jose Pons (Alicante University, Spain)
• 14:30
Physics of isolated neutron stars from their X-ray emission 20m
X-ray spectral properties of isolated neutron stars (magnetars, magnificient seven, CCOs, rotation-powered pulsars) carry precious information about the surface and inner temperature and magnetic field. An overview of the heterogeneous observational properties of the whole X-ray pulsar population is presented and used to constrain properties of the NS interior, surface and magnetosphere.
Speaker: Daniele Viganò
• 14:50
Statistical ages and the cooling rate of X-ray dim isolated neutron stars 20m
The cooling theory of neutron stars is corroborated by its comparison with observations of thermally emitting isolated neutron stars and accreting neutron stars in binary systems. An important ingredient for such an analysis is the age of the object, which, typically, is obtained from the spin-down history. This age is highly uncertain if the object's magnetic field varies appreciably over time. Other age estimators, such as supernova remnant ages and kinematic ages, only apply to few handful of neutron stars. We conduct a population synthesis study of the nearby isolated thermal emitters and obtain their ages statistically from the observed luminosity function of these objects. We argue that a more sensitive blind scan of the galactic disk with the upcoming space telescopes can help to constrain the ages to higher accuracy.
Speaker: Dr Ramandeep Gill (CITA (University of Toronto))
• 15:10
Probing the crusts of transiently accreting neutron stars 20m
In transient X-ray binaries, the crust of a neutron star becomes temporarily heated during accretion outbursts, while it subsequently cools in quiescence when accretion has ceased. This crustal cooling can be observed by studying the thermal X-ray emission from quiescent neutron stars with sensitive X-ray satellites. Comparing these observations with theoretical simulations provides a unique opportunity to gain insight into the heat production and thermal transport properties of the neutron star crust. I will present the latest observational results and challenges in this research field.
Speaker: Dr Nathalie Degenaar (University of Michigan)
• 15:30
Quiescent thermal emission of neutron stars in LMXBs 15m
The theoretical modeling of the thermal relaxation of the neutron star crust in low mass X-ray binaries may be used to establish constraints on the crust and envelope composition and transport properties, depending on the astrophysical scenarios assumed. I will show numerical simulations of the neutron star crust thermal evolution and compare them with inferred surface temperatures for five sources: MXB 1659-29, KS 1731-260, EXO 0748-676, XTE J1701-462 and IGR J17480-2446. I will also present stationary envelope models to be used as a boundary condition for the crustal cooling models, showing how to set constraints to the envelope composition depending on the accretion mass rate. The evolution of MXB 1659-29, KS 1731-260 and EXO 0748-676 can be well described within a deep crustal cooling scenario while XTE J1701-462 and IGR J17480-2446 can only be explained with models beyond crustal cooling, for which I will present alternative scenarios.
Speaker: Dr Deborah Aguilera (Deutsches Zentrum fuer Luft- und Raumfahrt e.V., Bremen, Germany)
• 14:30 15:45
Afternoon session - Parallel B
Convener: Nanda Rea ((CSIC-IEEC Barcelona/University of Amsterdam))
• 14:30
Radio pulsar emission and crustal field evolution 20m
Models of pulsar radio emission that are based on an inner accelerating region require the existence of very strong and small scale surface magnetic field structures at or near the canonical polar cap. The aim of this paper is to identify a mechanism that creates such field structures and maintains them over a pulsar's lifetime. The likely physical process that can create the required 'magnetic spots' is the Hall drift occurring in the crust of a neutron star. It is demonstrated, that the Hall drift can produce small scale strong surface magnetic field anomalies (spots) on timescales of $10^4$ years by means of non-linear interaction between poloidal and toroidal components of the subsurface magnetic field. These anomalies are characterized by strengths of about $10^{14}$ G and curvature radii of field lines of about $10^6$ cm, both of which are fundamental for generation of observable radio emission.
Speakers: Prof. Gogi Melikidze (University of Zielona Gora) , Prof. Janusz Gil (University of Zielona Gora) , Prof. Ulrich Geppert (DLR and University of Zielona Gora)
• 14:50
The tormented quiescence of the transient neutron star low mass X-ray binary Centaurus X-4 20m
In low mass X-ray binaries a compact object, a black hole or a neutron star, is coupled with a late-type companion star, with mass lower than that of the Sun. Many low mass X-ray binaries are transient and they spend the bulk of their time in the so-called quiescent state, where their X-ray emission is low, just a tiny fraction of the Eddington luminosity. But, the physical mechanisms involved during quiescence are still debated. Several models have been proposed, but so far, a unifying scenario which can make a clear prediction, systematically matching the spectral energy distribution from Radio up to the X-ray emission of both NS and BH quiescent low-mass X-ray binaries, is still missing. Moreover, an increasing number of low mass X-ray binaries display evidence of variability in quiescence, the origin of which is still unclear. Residual accretion at very low Eddington luminosity rates could play an important role, however its physics is poorly understood. With the main goal of unveiling the real nature of the quiescent variability in low mass X-ray binaries containing a neutron star I planned a unique study of the best quiescent target: the neutron star Cen X-4. I conducted a multi wavelength (optical, ultraviolet, and X-ray) long-term monitoring (months) of the source on a daily basis. This allowed for the very first time to accurately characterize the variability properties of Cen X-4, and to show that it is still accreting also in quiescence. I will discuss the implication of the results on the physical status of the inner accretion flow.
Speaker: Federico Bernardini (w)
• 15:10
X-ray observations of gamma-ray pulsars detected by Fermi 20m
In this talk, we present the outcome of X-ray and optical/IR observations of gamma-ray pulsars detected by Fermi, as a part of a program aimed at completing the multi-wavelength coverage of these sources. We found X-ray counterparts for five Fermi pulsars, and we observed in X-ray some unidentified Fermi sources believed to be isolatd neutron stars.
Speaker: Dr Roberto Mignani (INAF/IASF)
• 15:30
Searching for pulsars with Einstein@Home 15m
The distributed computing project Einstein@Home searches for unknown pulsars in large data sets. So far, more than 350,000 volunteers from the world-wide public have signed up their computers to run scientific analyses with their spare cycles, reaching a teraflop peak performance. Einstein@Home was originally created to search for continuous gravitational waves (GWs), but is now also analysing radio and gamma ray data. The latest published Einstein@Home analysis of 2005-2007 data from the interferometric GW observatory LIGO has returned the most stringent all-sky upper limits on GW emission from isolated neutron stars. While LIGO is being upgraded, analysis of the 2009-2010 data set is still ongoing. An Einstein@Home all-sky search is currently in the post-processing stage, while a directed search for the supernova remnant Cassiopeia A is running on the volunteer computers. An Einstein@Home all-sky search is also envisaged as a flagship analysis for the Advanced LIGO era. Meanwhile, analyses of electromagnetic data have already been successful at discovering previously unknown pulsars, with 48 found in radio data from Arecibo and Parkes and another 4 in gamma ray data from the Fermi space telescope.
Speaker: David Keitel (Albert Einstein Institute)
• 15:45 16:15
Coffee break 30m
• 16:15 17:15
Evening session - Parallel A
Convener: Nathalie Degenaar (Ann Arbor, Michigan Univ., USA)
• 16:15
Neutron stars with hyperon cores: stellar radii and EOS near nuclear density 20m
We study the impact of the presence of a hyperon core on the R-M relation for neutron stars (NS). Using observational constraint Mmax>2Msun, and available EOSs, we show difference between R-M relation in the mass range 1.2 - 1.6 Msun between NS with nucleon cores and those based on EOS that allow for sizable hyperon cores in high mass NS. We find correlation between pressure at normal nuclear density n_0 and R(1.4Msun) and we critically discuss arguments against the presence of hyperon cores in massive NS. We argue that future LOFT mission with better than 5% precision of measuring simultaneously R and M of NS in some X-ray sources will have potential to rule out sizable hyperon cores in NS.
Speaker: Prof. Pawel Haensel (Nicholaus Copernicus Astronomical Centre, Warsaw, Poland)
• 16:35
The neutron star radius and the dense-matter equation of state 20m
A physical understanding of the behaviour of cold ultra-dense matter - at and above nuclear density - can only be achieved by the study of neutron stars, and the thermal emission from quiescent low-mass X-ray binaries inside globular clusters have proven very useful for that purpose. The recent 1.97±0.04 Msun measurement for the radio pulsar PSR 1614-2230 suggests that strange quark matter and hyperons/kaons condensate equations of states (EoS) are disfavoured, in favour of hadronic "normal matter" EoSs. Over much of the neutron star mass-radius parameter space, "normal matter" EoSs produce lines of quasi-constant radii (within the measurement uncertainties, of about 10%). We present a simultaneous spectral analysis of several globular cluster quiescent low-mass X-ray binaries where we require the radius to be the same among all neutron stars analyzed. The Markov-Chain Monte-Carlo method and the Bayesian approach developed in this analysis permits including uncertainties in the distance, in the hydrogen column density, and possible contributions to the spectra due to un-modelled spectrally hard components. Our results suggest a neutron star radius much smaller than previously reported, with a value Rns = 9.1±1.4 km, at 90% confidence, using conservative assumptions, which suggests that neutron start matter is best described by the softest "normal matter" equations of state.
Speaker: Sebastien Guillot (M)
• 16:55
The birth of quark stars 20m
The possible existence of two families of compact stars, neutron stars and quark stars, naturally leads to a scenario in which a conversion process between the two stellar objects occurs with a consequent release of energy of the order of 10^53 erg. We discuss recent hydrodynamical simulations of the burning process and neutrino diffusion simulations of cooling of a newly formed strange star. We also discuss this scenario in connection with recent measurements of masses and radii of compact stars.
Speaker: Giuseppe Pagliara
• 16:15 17:15
Evening session - Parallel B
Convener: Ulrich R.M.E. Geppert (DLR)
• 16:15
Gamma-ray emission and variability of the Crab Nebula above 100 MeV: theoretically challenging AGILE observations 15m
AGILE is an Italian Space Agency (ASI) space mission, built and operated in cooperation with INAF, INFN and CIFS, dedicated to the observation of the gamma-ray Universe in the 30 MeV - 50 GeV energy range, with simultaneous X-ray imaging capability. The AGILE satellite, launched on April 23rd, 2007, is substantially contributing to improve our knowledge on gamma-ray sources. I will summarize recent AGILE highlights on neutron-star systems and their surroundings, focusing in particular on the ground-breaking discovery of strong and rapid gamma-ray flares from the Crab Nebula over daily timescales. This discovery challenges emission models of pulsar wind and particle acceleration processes, and it won to the AGILE PI and the AGILE Team the Bruno Rossi Prize for 2012 by the High Energy Astrophysics division of the American Astronomical Society (AAS).
Speaker: Carlotta Pittori (ASDC and INAF-OAR)
• 16:30
Optical companions to binary Millisecond Pulsars in Globular Clusters: the case of IGR J18245-2452/PSR J1824-2452I 15m
The identification of the optical companions to binary millisecond pulsars (MSPs) is fundamental to characterize the formation and evolutionary processes of these exotic objects and to constrain the neutron star mass. In Globular Clusters (GCs) it also represents a crucial tool for quantifying the occurrence of dynamical interactions and understanding the effects of high stellar densities on the evolution of binaries. In this context I will present the main results recently obtained with the use of HST images that allowed us to succesfully increase the number of identified companions to MSPs in GCs. In particular, I will focus my attention to the optical companion to the transient IGR J18245-2452/PSR J1824-2452I in the GC M28.
Speaker: Cristina Pallanca
• 16:45
Millihertz Quasi-periodic Oscillations in 4U 1636-536: Pulse Profile and Energy Spectrum 15m
4U 1636-536 is a well-studied LMXB, consisting of a neutron star in a 3.8 hr orbit with a companion star of about 0.4 solar mass. The X-ray source shows the full range of rapid time variability, among them, burst oscillations and mHz QPOs are associated with thermonuclear burning on the neutron star. We performed a variability study of archival broadband X-ray observations of 4U 1636-536 and investigated the energy dependence of the mHz QPOs. Here we present the results of our waveform analysis and phase resolved spectral investigations and discuss implications of mHz QPO as a thermonuclear burning mode on the neutron star.
Speaker: Dr Holger Stiele (Shanghai Astronomical Observatory)
• 17:00
X-ray Bursts from Accreting Neutron star LMXBs 15m
Intense X-ray bursts (type-I bursts), originating from unstable thermonuclear conflagration, are observed from the surfaces of many accreting neutron star Low Mass X-ray Binary (LMXB) systems and are useful tools to constrain the equation of state and probe strong gravity regime. A series of such X-ray bursts were observed during the 2010 outburst of the transient pulsar IGR J17480-2446. These bursts were quite unique in nature, due to their smoothly varying periodicity with the shortest recurrence time observed till date and the lack of cooling during decay. The atypical nature of these bursts suggested them to be the type-II bursts originating from accretion disc instability and thus raises questions regarding the origin of mHz QPOs observed at the outburst peak. Using Rossi X-ray Timing Explorer (RXTE) PCA data, we show that the bursts are indeed of thermonuclear origin and confirm the quasi-stable nuclear burning model of mHz QPOs. This transient source is only the second source to show atoll-Z transition and it spans a large intensity range during the outburst showing hysteresis in the Hardness-Intensity Diagram (HID). From the study of the spectral state evolution of this source during the outburst, we show that the burst properties are highly correlated with accretion and thus the evolution of the properties of the highly frequent bursts with spectral states offers the perfect laboratory to study thermonuclear ignition mechanism and the physics of recurrent bursts.
Speaker: Manoneeta Chakraborty (Tata Institute of Fundamental Research)
• 20:00 23:59
Conference dinner 3h 59m
• Friday, 28 March
• 09:00 10:20
Plenary session 11
Convener: Deepto Chakrabarty (M)
• 09:00
Review talk on numerical modelling of neutron star coalesence and their remnants. 40m
Review talk on numerical modelling of neutron star coalesence and their remnants.
Speaker: Dr Hans Thomas Janka (MPI Garching)
• 09:40
Continuous gravitational waves and neutron star microphysics 40m
Mechanisms of continuous gravitational-wave emission from neutron stars include long-lived r-mode oscillations and rotations of static deformations (“mountains”). Emission depends on the equation of state and transport coefficients of matter above nuclear density. Therefore gravitational-wave searches may be guided by, and reveal information on, the equation of state and other properties of dense matter. I give a brief survey of what we know about the links in both directions, and speculate about the prospects as the advanced interferometers come on-line.
Speaker: Prof. Benjamin Owen (Penn State, USA)
• 10:20 10:50
Coffee break 30m
• 10:50 12:10
Plenary session 12
Convener: Deepto Chakrabarty (M)
• 10:50
MAGNETIC FIELDS IN RELATIVISTIC COMPACT-OBJECT BINARIES 40m
I will review the recent progress made in modelling binaries of compact objects and the role played by magnetic fields in their evolution. Special attention will be paid to binary neutron stars and to highlighting how the progress of ab-initio fully relativitistic calculations can be used to several aspects of the phenomenology of short gamma-ray burst.
Speaker: Prof. Luciano Rezzolla (AEI)
• 11:30
Extracting information on the neutron star equation of state via gravitational waves from binary inspirals 40m
Binary neutron stars and neutron star-black hole systems are some of the most promising sources for gravitational-wave observations with Advanced terrestrial interferometer detectors. For such systems, the matter contributes to the spacetime dynamics, leaving an imprint on the gravitational radiation from the system. I will discuss how we can understand and model this imprint, so that we can use it to constrain our understanding of the properties of dense matter. I will also outline aspects requiring further work.
Speaker: Dr Tanja Hinderer (Caltech, USA)
• 12:10 14:00
Lunch break 1h 50m
• 14:00 16:00
Afternoon session - Parallel A
Convener: Andrew Melatos (University of Melbourne, Australia)
• 14:00
Equation-of-state dependence of neutron-star mergers 20m
By a representative set of hydrodynamical simulations we investigate the influence of the high-density equation of state on observable features of neutron-star mergers. The dependence of the gravitational-wave emission on the equation of state of neutron-star matter is addressed. On the basis of our survey we point out a novel possibility to determine neutron-star radii from gravitational-wave detections of the postmerger phase of a neutron-star coalescence. This idea is based on the observation that the dominant oscillation frequency of the merger remnant correlates with the radii of neutron stars. The analysis also reveals constraints on other properties of neutron stars and the equation of state. The likelihood of a corresponding gravitational-wave observation is estimated. Moreover, nucleosynthesis calculations are presented showing a robust rapid neutron-capture process in the matter becoming gravitationally unbound by neutron-star collisions. The properties of optical transients which are powered by the radioactive decay of the freshly synthesized elements, are discussed as well. Also from these possibly observable signals information on the equation of state may be inferred.
Speaker: Dr Andreas Bauswein (Department of Physics, Aristotle University of Thessaloniki)
• 14:20
Results of the search for continuous gravitational wave signals from known pulsars 20m
A spinning neutron star, if asymmetric respect to the rotation axis, is expected to emit a continuous gravitational wave signal. In this talk I present a summary of the results obtained in the analysis of LIGO and Virgo data searching for continuous gravitational wave signals emitted by known pulsars. I focus attention on the astrophysical interpretation of the most interesting upper limits so far established and on the importance of the input from photon astronomy. Prospects for the advanced detector era are also discussed.
Speaker: Dr Cristiano Palomba (INFN Roma)
• 14:40
Compact static stars in minimal dilatonic gravity 20m
We present the basic equations and relations for the relativistic static spherically symmetric stars (SSSS) in the model of minimal dilatonic gravity (MDG) which is locally equivalent to the f(R) theories of gravity and gives an alternative description of the effects of dark matter and dark energy. The results for a simplest form of relativistic equation of state (EOS) of neutron matter are represented. Our approach overcomes the well known difficulties of the physics of SSSS in f(R) theories of gravity introducing two novel EOS for cosmological energy-pressure densities and dilaton energy-pressure densities, as well as proper boundary conditions.
Speaker: Dr Plamen Fiziev (Foundation of Theoretical and Computational Physics and Astrophysics (TCPA) Sofia University)
• 15:00
Measuring the Mass-Radius Relation of Neutron Stars with the Large Observatory for X-ray Timing (LOFT) 20m
High-time-resolution and spectroscopic X-ray observations of compact objects provide access to strong-field gravity, the equation of state of ultra-dense matter and black hole masses and spins. A 10 m^2-class instrument in combination with good energy resolution is required to exploit diagnostics and answer two of the fundamental questions of the European Space Agency (ESA) Cosmic Vision Theme "Matter under extreme conditions", namely: does matter orbiting close to the event horizon follow the predictions of general relativity? What is the equation of state of matter in neutron stars? The Large Observatory For X-ray Timing (LOFT) has been designed to answer these questions; it has been extensively studied in the last 3 years and will be proposed to ESA in response to the forthcoming M4 call. The Large Area Detector (LAD) on board LOFT will have an effective area of ~10 m^2 (more than an order of magnitude larger than any spaceborne predecessor) in the 2-30 keV range, coupled with a CCD-class spectral resolution of ~240 eV (providing a two orders of magnitude higher throughput than any previous instrument solid state instrument). The LAD will yield unprecedented information on the mass-radius relation of neutron stars and on strongly curved spacetimes.
Speaker: Prof. Luigi Stella (INAF - OAR)
• 15:20
On the gravitational signal from tidally deformed neutron stars in coalescing binaries 20m
The gravitational signal emitted in the late inspiral of a binary system, composed by a neutron star and another compact object, encodes the deformability properties of the neutron star, which depend on the behaviour of matter in the stellar interior. We discuss how the detection of this signal from ground based interferometers of second and third generation, can be used to extract information on the neutron star equation of state.
Speaker: Prof. Leonardo Gualtieri (Rome University "La Sapienza", Italy)
• 15:40
Probing the neutron star equation of state with second-generation gravitational wave detectors 20m
Fisher matrix and related studies have suggested that with second-generation gravitational wave detectors, it may be possible to infer the equation of state of neutron stars using tidal effects in binary inspiral. Here we present the first fully Bayesian investigation of this problem. We simulate a realistic data analysis setting by performing a series of numerical experiments of binary neutron star signals hidden in detector noise, assuming the projected final design sensitivity of the Advanced LIGO- Virgo network. With an astrophysical distribution of events (in particular, uniform in co-moving volume), we find that only a few tens of detections will be required to arrive at strong constraints, even for some of the softest equations of state in the literature. Thus, direct gravitational wave detection will provide a unique probe of neutron star structure.
Speaker: Michalis Agathos
• 14:00 16:00
Afternoon session - Parallel B
Convener: Janusz Gil (University of Zielona Gora, Poland)
• 14:00
Multiwavelength properties of gamma-ray loud binaries. 15m
Gamma-ray-loud binary systems are a newly identified class of X-ray binaries detected up to TeV energies. They are peculiar examples of the HMXBs with the energy output dominated by emission in the high-energy (GeV) gamma-ray band. The nature of this peculiarity is not completely understood yet. At least one system, PSR B1259-63 is known to be powered by a young pulsar. The nature of the compact objects orbiting massive stars in other systems is not constrained. However, similarity of the spectral characteristics of the known gamma-ray binaries (only 4 are currently known) suggests similar nature of the compact objects in these systems. In my talk I will review the latest multi-wavelengths observations of these systems and discuss possible theoretical scenarios.
Speaker: Maria Chernyakova (D)
• 14:15
Radiation efficiencies of the pulsars (current update). 15m
Eighteen pulsars with optical counterparts or with significantly deep upper limits on the optical luminosity are known currently. Using available multi-wavelength data for these pulsars we reanalyze the efficiencies of the conversion of the pulsar spin-down power into the observed non-thermal luminosity L in different spectral domains. This sample of pulsars confirms the non-monotonic evolution of the pulsar radiation efficiency in the optical and X-ray domains (Zharikov et al. 2006). There is a clear evidence of a change in the behavior of the optical and X-ray efficiencies around ~ 10^4 years. Optical and X-ray efficiencies initially decrease before starting to flatten or increase at larger ages. The timescale ~10^4 years is comparable to the transition between neutrino and photon cooling stage (Yakovlev et al. 2004, and references therein) in neutron stars. The change of the cooling stage probably affects the distribution of relativistic particles in the pulsar magnetosphere, which is reflected in the dependence of the optical/X-ray efficiency on the pulsar age. The slopes of the time evolution of optical and X-ray efficiencies after 10^4 years are practically similar and compatible with that of radio efficiency.
Speaker: Sergey Zharikov
• 14:30
Constraint of Pulsar Wind Properties from Induced Compton Scattering off Radio Pulses 15m
Pulsar winds have problems in energy conversion and pair-cascade processes which determine the magnetization, the pair multiplicity and the bulk Lorentz factor of the wind. We study induced Compton scattering by a relativistically moving cold plasma to constrain wind properties by imposing that radio pulses from the pulsar itself are not scattered by the wind as was first studied by Wilson & Rees. We find that relativistic effects cause a significant increase or decrease of the scattering coefficient depending on scattering geometry. Applying the Crab pulsar wind, we obtain the lower limit of the bulk Lorentz factor of ~ 10 at the light cylinder when the wind velocity is significantly inclined with respect to the radio pulses. Considering the lower limit of the pair multiplicity 10^6.6 suggested by recent studies of the Crab Nebula, the large inclination angle of the wind velocity (order unity), the small size of radio pulse emission region (~ 10^3 cm) and the small magnetization parameter (order unity) are required for the pair multiplicity > 10^6.6.
Speaker: Dr Shuta Tanaka (Institute for Cosmic Ray Research, The University of Tokyo)
• 14:45
g-modes in superfluid neutron stars 15m
We show that, contrary to general belief, g-modes can exist in superfluid neutron stars. Unlike ordinary composition g-modes in cold non-superfluid neutron stars, these g-modes turn out to be very temperature-dependent and can have frequencies up to ~0.5 kHz. We analyze their properties and briefly discuss the ways they can be excited. Possible observational signatures of the proposed g-modes are also examined. This work was partially supported by RF president programme (grants MK-506.2014.2), by RFBR (grants 11-02-00253-a and 14-02-31616-mol-a), by the Dynasty Foundation, and by the Ministry of Education and Science of Russian Federation (Agreement No.\ 8409, 2012).
Speaker: Elena Kantor
• 15:00
The first variable gamma-ray pulsar: challenging the models of high-energy magnetospheric emission 15m
Pulsar variability, including mode changes and intermittent behavior, is a powerful probe of neutron star magnetospheres and represents a challenge for current emission models. In the gamma-ray domain where the bulk of their spindown luminosity is radiated, however, pulsars were believed to be steady emitters on timescales longer than those needed for their detections. Surprisingly, Fermi observed a 20% flux decrease in PSR J2021+4026 near 2011 October 16th (MJD 55850), over a time scale shorter than a week. At the same time, the spindown rate increased by 4% and there were significant changes in the pulse profile. We speculate that the flux change is due to a modification in the emission beaming precipitated by a shift in the magnetic field structure, leading to a change of either effective magnetic inclination or effective current. This “jump” of PSR J2021+4026 breaks the axiom of pulsars as steady gamma-ray emitters, opening new avenues for investigating pulsar magnetospheres through variability studies at gamma-ray energies.
Speaker: Massimiliano Razzano
• 15:15
Linkup of non-rotating neutron-star and outer-Schwarzschild metrics 15m
Neutron stars (NSs) are the compact objects with the metrics detectably deviated from the flat spacetime. In the interior of every NS the metrics can be calculated from the model of its internal structure. In the surrounding empty space the metrics is described by the outer Schwarzschild solution (OSS) of Einstein field equations if a non-rotating NS is considered. In the linkup of both NS and OSS metrics, made in the outer physical radius of the NS, the components of metric tensor should be the continuous functions of radial coordinate. We deal with this linkup in the case of the simple Oppenheimer-Volkoff model of NS, in our contribution. We point out that the linkup occurs to be a non-trivial task and suggest a way, which enables to achieve the success. The continuity of metrics should be the demonstrated in each realistic model of NS.
Speaker: Dr Lubos Neslusan (Astronomical Institute, Slovak Academy of Sciences)
• 15:30
Statistical measure of complexity in compact stars with global charge neutrality 15m
Recently, it has been suggested that a critical electrical field arises during the gravitational collapse of massive stars leading to a vacuum polarization. This, in turn, leads to the necessity of a reexamination of the gravito-electrodynamical properties of compact stars of the class of neutron stars. Rotondo, Rueda, Ruffini and Xue claim to have proved the impossibility of local charge neutrality and then solved the coupled system of the general relativistic Thomas-Fermi-Einstein-Maxwell equations for the structure of neutron stars. Within the same approach of Avellar and Horvath (2012) we have calculated how the global neutrality hypothesis affects the order/disorder of these systems for a simple equation of state. We show the relative preference of local vs. global conservation in terms of the obtained information content of the systems under consideration.
Speaker: Mr Rodrigo Souza (IAG - USP Sao Paulo)
• 16:00 16:30
Coffee break 30m
• 16:30 18:00
Evening session - Parallel A
Convener: Leonardo Gualtieri (Rome Univ., Italy)
• 16:30
Instability windows and evolution of rapidly rotating neutron stars 20m
We consider an instability of rapidly rotating neutron stars in low-mass X-ray binaries with respect to excitation of r-modes. We argue that finite temperature effects in the superfluid core of a neutron star lead to a resonance coupling and enhanced damping (and hence stability) of oscillation modes at certain stellar temperatures. We demonstrate that neutron stars with high spin frequency spend substantial amount of time at these resonance' temperatures. This finding allows us to explain puzzling observations of hot rapidly rotating neutron stars in low-mass X-ray binaries. It also imposes a new theoretical limit on the neutron star spin frequency, explaining the cut-off spin frequency ~730 Hz, following from the statistical analysis of accreting millisecond X-ray pulsars. Besides explaining the observations, our model provides a new tool to constrain superdense matter properties comparing measured and theoretically predicted resonance temperatures. This work was partially supported by RF president programme (grants MK-506.2014.2), by RFBR (grants 11-02-00253-a and 14-02-31616-mol-a), by the Dynasty Foundation, and by the Ministry of Education and Science of Russian Federation (Agreement No.\ 8409, 2012).
Speaker: Mikhail Gusakov
• 16:50
New possible class of rapidly rotating neutron stars 15m
We discuss a new hypothetical class of neutron stars dubbed HOFNARs' (HOt and Fast Non-Accreting Rotators) or hot widows' (similar to black widow' pulsars) which are hot and fast-rotating, but do not accrete matter. These sources are unstable with respect to r-modes and are formed in low-mass X-ray binaries (LMXBs), after exhausting the low-mass companion. Their high temperatures are maintained by r-mode dissipation; as we show they can stay hot during a very long period of time ~10^9 yrs. Hot widows'/HOFNARs can be observed as X-ray sources with purely thermal neutron star atmosphere spectrum, which perfectly matches spectral identification criteria for quiescent LMXBs (qLMXBs) candidates in globular clusters. This means that some of X-ray sources known as qLMXB candidates can in fact be Hot widows'/HOFNARs. An existence of Hot widows'/HOFNARs might allow (i) to explain overproduction of millisecond pulsars in population synthesis models of globular clusters; (ii) to lower estimates of recurrence time for qLMXB candidates in globular clusters to theoretically predicted value. We discuss identification criteria for `Hot widows'/HOFNARs and analyze a variety of possibilities, which they give to constrain dense matter properties. This work was partially supported by RF president programme (grant MK-506.2014.2), by RFBR (grant 14-02-31616-mol-a), by the Dynasty Foundation, and by the Ministry of Education and Science of Russian Federation (Agreement No.\ 8409, 2012).
Speaker: Andrey Chugunov (I)
• 17:05
Magnetic fields and r-modes in slowly rotating relativistic neutron stars 20m
We study here the r-modes in the Cowling approximation of a slowly rotating and magnetized neutron star with a poloidal magnetic field, where we neglect any deformations of the spherical symmetry of the star. We were able to quantify the influence of the magnetic field in both the oscillation frequency of the r-modes and the growth time of the gravitational radiation emission. We conclude that magnetic fields of the order 10^{15} G at the center of the star are necessary to produce any changes.
Speaker: Cecilia Chirenti (UFABC)
• 16:30 18:00
Evening session - Parallel B
Convener: Luigi Stella (INAF - Osservatorio di Roma)
• 16:30
Simulations of X-ray Bursts and Superbursts 15m
Neutron stars in low mass X-ray binary systems with an accretion flow of matter from the companion star have been observed to exhibit regular bursts. These so-called type I X-ray bursts are thermonuclear explosions occurring in the surface layers of neutron stars. After thousands of type I X-ray bursts, enough ashes have been accumulated and a rare superburst event may take place. Such an event is thought to be triggered by unstable burning of carbon. However, most theoretical models of superbursts are not able to reproduce the observed behaviour. We present a one-dimensional model which simulates thousands of type I X-ray bursts in the surface layer of an accreting neutron star. To investigate this scenario, our code couples general relativistic hydrodynamic with a nuclear reaction network. Therefore, we are able to predict the evolution of the composition of the ashes, which has strong implications on the ignition of superbursts. Furthermore, we give an estimate for the heat source which is needed to trigger a superburst. We find that self-consistent simulations of superbursts are challenging and need further investigations.
Speaker: Ms Sofie Fehlmann (University of Basel)
• 16:45
Testing the Impact of Surface Temperature Inhomogeneities on Quiescent Neutron Star Mass/Radius Determinations 15m
Spectral analyses of quiescent neutron stars in X-ray binaries have been used to constrain the mass and radius of the neutron stars. A question not yet explored is the effect of undetected hot spots on the spectrum, and thus on the inferred mass and radius of a quiescent neutron star. We simulate light curves for hydrogen atmosphere neutron stars with hot spots, performing Monte Carlo simulations to infer the range of likely pulsation amplitudes detectable for given choices of hot spot temperature and radius. We search for pulsations in the deepest observations of quiescent neutron stars done so far, X7 and X5 in the 800-ks Chandra HRC observations of 47 Tuc, finding 3-sigma upper limits on the pulsed fraction of 17.5% and 18.9% respectively for spin periods as low as 1.5 ms, and including acceleration searches. We will use these limits to constrain the size and/or temperature of any hot spots on these quiescent neutron stars. Finally, we plan to use these constraints to study the effects on the X-ray spectrum, and thus on the inferred mass and radius, that these possible hot spots might produce.
Speaker: Mr Khaled Elshamouty (University of Alberta)
• 17:00
New multiwavelength observations of two gamma-ray pulsars J0357+3205 and J1357-6429 15m
Recent discoveries of the Fermi mission have increased the number of known gamma-ray pulsars by a factor of twenty. Multiwavelength investigations of these objects are crucial for unveiling the pulsar emission nature. Because gamma-ray pulsars are typically nearby and energetic, they, in particular, appear to be promising targets for studies in X-ray and optical domains. We present new observations of two gamma-ray pulsars J0357+3205 and J1357-6429 obtained with GTC/OSIRIS and VLT/NACO facilities. We also performed an independent analysis of the archival X-ray data obtained with XMM-Newton/EPIC and Chandra/ACIS. For the radio quiet pulsar J0357+3205 we set a deep upper limit g>28.1 on its brightness in the optical and compare it with the X-ray data. The upper limit implies that the optical nonthermal power-law emission of the pulsar is about two orders of magnitude lower than it was expected from the X-ray data and suggests a spectral break in the pulsar nonthermal spectrum between the optical and X-rays. At the same time the optical upper limit is consistent with the upper limit on the temperature of the neutron star entire surface of 40 eV followed from the X-ray data, making it one of the coldest among cooling middle-aged neutron stars known and a promising target for observations in the UV. For the pulsar J1357-6429 we present new adaptive-optical near-IR observations and discuss possible counterpart candidates of the object. New radio interferometric ATCA observations are also presented. They allow us to put new constraints on the pulsar proper motion.
Speaker: Ms Aida Kirichenko (Ioffe Physical Technical Institute)
• 17:15
New results of the time lags in the QPO's of 4U 1636-53 15m
We present an analysis of the energy and frequency dependence of the Fourier time lags of the hectoHertz quasi-periodic oscillations (QPOs) and of the QPOs at the frequency at which the power density spectrum shows a break in the neutron-star low-mass X-ray binary 4U 1636−53, using a large data set obtained with the Rossi X-ray Timing Explorer. We found that: (i) For the break frequency QPO: for low frequencies, in general the time lag is positive, but it is decreasing with increasing frequency, reaching zero lag at ~ 20 Hz. Between 20 and 35 Hz there is a small fluctuation around zero, from where the time lags become positive again and increase slightly above zero up to 65 Hz. (ii) For the hHz QPO: we see that when the frequency is ~100 Hz the time lag is negative, but it increases to zero already at ~110 Hz, being consistent with this value up to 130 Hz from where it increases to 0.5 msec at around 140 Hz. From 140 Hz the time lag decreases sharply, being strongly negative for hHz > 220 Hz. (iii) We see no significant dependence of the time lags on energy for both QPOs studied here, but for the hHz there can be some weak sinusoidal dependence. We compare these lags with our previous results for the lags of the kiloHertz QPOs in this same source and discuss possible scenarios for producing the lags in this system in the context of reflection off the accretion disc or up-/down-scattering in a hot medium close to the neutron star.
Speaker: M. Bronzato de Avellar (IAG in San Paulo, Brasil)