Annual NewCompStar Conference 2015

15 Jun 2015, 08:00 → 19 Jun 2015, 14:00 Europe/Budapest

Mátyas Hall (Hotel Mercure Buda, Budapest)

Gergely Gábor Barnaföldi (Wigner RCP RMI of the Hungarian Academy of Sciences) , Mátyás Vasúth (MTA Wigner FK) , Péter Kovács (KFKI RMKI)

Welcome!

This international conference is devoted to all aspects of compact stars and related fields, such as physics of dense matter, nuclear astrophysics, pulsars and binary neutron stars, gravitational physics and cosmology. This year the event is organized by the Wigner Research Centre for Physics of the Hungarian Academy of Sciences, the largest physics research center in Hungary.

The scientific program includes plenary talks from invited speakers as well as standard talks chosen from the abstracts of registered participants by the organizing committee.  The plenary talks will group around six main topics as follows,

 

• Equation of State of Hot and Dense Matter
• Neutronstar evolution and Neutronstar cooling 
• Nucleosynthesis and Supernova Physics
• Pulsars and Observation
• Magnetars and Gamma Ray Bursts
• Gravitational Waves, Cosmology and Alternative theories

Conference Plenary speakers:

 

• Mehmet Ali Alpar  (Sabanci University) 
• Nils Anderson  (University of Southampton)
• Almudena Arcones  (Darmstadt TU)
• Maria Grazia Bernardini  (INAF - Osservatorio Astronomico di Brera)
• Fiorella Burgio  (INFN Catania)
• Valeria Ferrari  (Universita di Roma La Sapienza)
• Francesca Gulminelli  (LPC Caen France)
• Oleg Kargaltsev  (The George Washington University)
• Kostas Kokkotas  (Eberhard-Karls University of Tubingen)
• Andrew Melatos  (University of Melbourne)
• Sandro Merghetti (INAF, IASF-Milano)
• Rosalba Perna  (Stony Brook University)
• Jose Pons (Universitat d'Alacant)
• Michele Punturo (INFN Perugia)
• Chihiro Sasaki  (FIAS - University of Frankfurt)
• Andreas Schmitt  (TU Wien)

Registration procedure (very important!)

1. Conference page registration: First you should regrister for the conference page, under the 'Registration tab' on the left side. This is needed for us to keep track of each participant
2. Indico registration, abstract submission: In order to submit an abstract you should register to the Indico, which can be done in the 'Submit Abstract' tab on the left or here. After the Indico registration you can upload your abstract
3. Registration for payment options, student support:  Conference fee payment is possible through a secure site of our conference organization company, which can be found in the 'Conference fee payment' tab on the left or here. Due to additional security a separate registration is needed! It is possible to pay by bank transfer, by credit card, or in cash at the conference site.  Either way you should register there. Very important: You can only get a receipt if you registered here! For sudent support you should check the box named 'Hereby I apply for a student support'. If you apply you will be noticed about your possible support in due time.

The Conference fee is 290 €. 

Since the conference will be at Hotel Mercure Buda we have special prizes for the participants, which are 72 €/night for single room and 82 €/night for double room in case of four nights stay and includes breakfasts. The buffet lunch at the hotel costs 23 €/day.  
 
The conference dinner will be at Borkatakomba and its cost is included in the conference fee for participants, while it is 45 € for accompanying persons.

 

 

 

 

 

Slides BarnafoldiGG_NewCompStar_Closing_2015.pdf

Monday, 15 June

08:00 → 09:30 Registration

08:00 Registration

09:30 → 10:00 Opening

09:30 Greetings from Institute Director

Speaker: Peter Levai (WIGNER RCP)

09:40 Introducing the NewCompStar COST Action

Speaker: Prof. Luciano Rezzolla

Slides Luciano_Budapest_opening_0615.pdf

09:50 General remarks, greetings (organizers)

Speaker: Dr Gergely Gábor Barnaföldi (Wigner RCP RMI of the Hungarian Academy of Sciences)

Slides CompStar2015_Technikal_Informations.pdf

10:00 → 12:30 Plenary

10:00 Sub-saturation equation of state for Core-Collapse Supernovae and Neutron Stars

The construction of a realistic equation of state for dense matter as it can be found in core-collapse supernovae and neutron stars is a formidable task which is not yet completely achieved. The structure of very high density matter in the neutron star core is by far the most uncertain part of the EoS modeling. However, even in the least exotic regime of sub-saturation matter, where the degrees of freedom are purely nucleonic and relatively well-known, the presence of clustering due to the Coulomb quenching of the nuclear liquid-gas phase transition requires beyond mean-field methods properly treating all the complexity of nuclear structure, in a regime of neutron-rich matter where no experimental data exist to validate the available effective interactions. Self-consistent mean-field approaches with realistic effective interactions are still routinously applied at zero temperature. This is justified thanks to the Wigner-Seitz structure of stellar matter, which reduces the thermodynamic limit to a single nucleus problem. However, a consistent treatment at finite temperature in principle implies beyond mean-field configuration mixing. This is presently a problem since existing models are either done in the single nucleus approximation, or do not recover the single-nucleus Wigner-Seitz limit of zero temperature. In this talk we will present a density-functional formalism which, by introducing explicit cluster degrees of freedom, consistently describes the neutron-rich nuclei immersed in the gas of their continuum states in the inner crust, and the nuclear statistical equilibrium of different in-medium modified nuclear species in supernova matter. The influence of the effective interaction, and specifically the density dependence of the symmetry energy, will also be discussed.

Speaker: Prof. Francesca GULMINELLI (LPC and University of Caen)

Slides gulminelli_f.pptx

11:00 Coffee break

11:30 The many lives of magnetized neutron stars

The magnetic field strength at birth is arguably one of the most important properties to determine the evolutionary path of a neutron star. Objects with very high fields, collectively known as magnetars, are characterized by high X-ray quiescent luminosities, outbursts, and, for some of them, sporadic giant flares. While the magnetic field strength is believed to drive their collective behaviour, however, the diversity of their properties, and, especially, the observation of magnetar-like bursts from 'low-field' pulsars, has been a theoretical puzzle. In this talk, I will discuss results of long-term MHD simulations which, by following the evolution of magnetic stresses within the neutron star crust, have allowed to relate the observed magnetar phenomenology to the physical properties of the neutron stars, and in particular to their age and magnetic field strength and topology. The dichotomy of 'high-B' field pulsars versus magnetars is naturally explained, and occasional outbursts from old, low B-field neutron stars are predicted. I will conclude speculating on the fate of old magnetars.

Speaker: Rosalba Perna (Stony Brook University)

Animation B1e14.mpg B5e14.mpg

Slides CompStar2015_RosalbaPerna.pdf CompStar2015_RosalbaPerna.ppt

12:30 → 14:00 Lunch

12:30 Lunch

14:00 → 18:15 Parallel A: Neutronstars and Gravitational Waves

14:00 Early evolution of newly born proto-neutron stars

I have written a new code for the early evolution of a newly born neutron star (which is called proto-neutron star, PNS). At each step of the quasi-stationary PNS evolution, the code integrates the Tolman-Oppenheimer-Volkoff equations and then evolves the thermodynamical profiles solving the energy integrated neutrino diffusion equations. My final aim is to study the frequencies at which a PNS oscillates and emits gravitational waves. In particular, these frequencies depend on the presence of convection, on the high-density finite temperature equation of state of matter and the corresponding neutrino diffusion coefficients, and on the consequent PNS evolutionary path. This part of the work is still in progress.

Speaker: Mr Giovanni Camelio (University of Rome "Sapienza", Physics Department)

Animation GiovanniCamelio_animate.gif

Slides GiovanniCamelio_presentazione.pdf

14:25 Importance of stellar oblateness and relativistic effects on accretion disks around compact stars.

We present numerical calculations of orbital and epicyclic frequencies of nearly circular orbits around rotating neutron stars and strange quark stars. The FPS equation of state was used to describe the structure of neutron stars while the MIT bag model was used to model the equation of state of strange quark stars. All the uniformly rotating stellar configurations were computed in full general relativity. We find that the vertical epicyclic frequency and the related nodal precession rate of inclined orbits are very sensitive to the oblateness of rotating star. In particular, it has been shown that for rotating stellar models of moderate and high-mass strange quark stars, the sense of the nodal precession changes at a certain rotation rate (Gondek-Rosińska et al. 2014). As it turns out, a similar effect can be observed for rapidly rotating neutron stars.

Speaker: Mr Mateusz Wisniewicz (Kepler Institute of Astronomy)

Slides MateuszWisniewitz_pres_buda_mw.pdf

14:50 Deep crustal heating in accreting neutron stars.

Deep crustal heating phenomenon plays important role in explaining some thermal properties of accreting neutron stars. In soft X-ray transients (SXT) it is used to explain the relatively high luminosity of neutron star during quiescence, and in some transient X-ray sources to study the thermal relaxation from accreting to quiescent state. To determine the properties of a crust of accreting neutron stars we use the model of nuclei based on Brussels-Montreal nuclear energy density functional theory (BSk) and compare our results to the previous Compressible Liquid Drop Model (CLDM) ones. Although the total energy release per one accreted nucleon is similar, the location and number of the energy sources and corresponding energy release due to the non-equilibrium nuclear reactions depend on the specific properties of assumed model of nuclei such as a proton quantum shell corrections included in BSk models, which are absent in CLDM calculations. The influence of these effects on the thermal properties of accreting neutron stars is discussed.

Speaker: Dr Julian Leszek Zdunik (Nicolaus Copernicus Astronomical Center)

Slides zdunik.pdf

15:15 An overview of close binary systems containing (massive) neutron stars: the intermittent accretion disc phenomenon

We calculate the evolution of close binary systems (CBSs) formed by a neutron star (behaving as a radio pulsar) and a normal donor star, evolving either to a helium white dwarf (WD) or ultra short orbital period systems. Some of these systems are expected to evolve into so-called redback and black widow systems. The evolutionary tracks considered X-ray irradiation feedback and evaporation due to radio pulsar irradiation, usually dismissed in CBS evolution. We first show that irradiation feedback leads to cyclic mass transfer episodes, allowing CBSs to be observed in-between as radio pulsars with companions under conditions in which standard, non-irradiated models predict the occurrence of a LMXB. This behavior accounts for the existence of a family of binary systems known as redbacks. We found that, in general, CBSs with initial orbital periods ~ 1 day evolve into redback pulsars. Some of them produce low-mass helium WDs, and a subgroup withshorter Pi become black widows systems. Thus, some black widows may descent from redbacks, although not all redbacks evolve into black widows We also predict redback companions should almost fill their Roche lobe, as it is the case of PSR J1723-2837. This state is also possible for systems evolving with larger orbital periods. Therefore, binary radio pulsars with companion star masses larger than expected to produce helium WDs may also result in such quasi-Roche Lobe Overflow states, rather than hosting a carbon-oxygen WDs. This swelling is a direct consequence of the irradiation feedback. We finally present a calculation of the instability leading to the collapse/rebuilding of the accretion disc which depends heavily of the irradiation, showing that the timescale is a ~few years at most, in agreement with the recent observations. This shortening is only possible because of the incidence of X rays and complements the understanding of the evolution of these extreme systems.

Speaker: Dr Jorge Horvath (IAG-USP)

Slides JorgeHorvath_NewCompStar.pdf

15:40 Modified Urca processes in the BHF framework

We calculate the rate of neutrino emission due to modified Urca processes in a nucleon core of a neutron star taking into account in-medium effects on the nuclear interaction. The nuclear interaction is described via the in-medium G-matrix calculated in the Brueckner-Hartree-Fock framework with the continuous choice of the single particle potential. The full Argonne v18 potential with addition of the Urbana IX effective three-body forces is used. We find that the in-medium effects in this model considerably modify the reaction rates, and the modification becomes stronger for the densities closer to the direct Urca threshold. The implications of the results for the neutron star cooling are discussed.

Speaker: Dr Peter Shternin (Ioffe Institute)

Slides PeterShternin-Murca2015.pptx

16:05 Coffee Break

16:35 The unpairing effect in magnetars: cooling and rotational dynamics

I will describe the microphysics, phenomenology, and astrophysical implication of a B-field induced unpairing effect that may occur in magnetars, if the local B-field in the core of a magnetar exceeds a critical value Hc2. The focus will be on modification in the neutrino emissivities of neutron stars as well as their superfluid dynamics.

Speaker: Dr Armen Sedrakian (Institute for Theoretical Physics, Goethe University, Frankfurt am Main)

Slides SedrakianBuda2015.pdf

17:00 Neutrinos and neutrino-driven winds in the aftermaths of binary neutron star mergers.

Binary neutron star mergers are among the most extreme events happening in the Universe. These 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 the newly discovered kilo/macro-novae. Despite the central role played by neutrinos in this scenario, their role is still unclear and more investigations are required. In this talk, I will present results from 3D simulation of the aftermath of a binary neutron star merger. The dynamics of the disc will be investigated, as well as the neutrino emission coming from the central object and the innermost part of the accreting disc. The interaction between the disc and the neutrino radiation produces a neutrino-driven wind on a timescale of a few tens of milliseconds after the merger. Inside the wind, the electron fraction of the matter (initially extremely neutron rich) is reset by neutrino absorption. The properties of the related ejecta will be explored, with a special emphasis on the nucleosynthesis yields and on their dependences on microphysics inputs. Implication of the wind in terms for the central engine of short GRBs will also be discussed.

Speaker: Albino Perego (TU-Darmstadt)

Slides AlbinoPerego_presentation.pdf

17:25 The gravitational wave signal from ensemble of the neutron stars

Rotating neutron stars are likely sources of gravitational radiation for Advanced Virgo and Ligo detectors. We calculated the gravitational waves background produced by the neutron stars in the Milky Way. To determine the signal we adopt a realistic model of the population of neutron stars taking into account the evolution of the rotation period and the magnetic field of each star. The position and velocity of each pulsar is obtained by calculating its motion in the gravitational potential of the Galaxy. We analyse the intensity in the sky and the spectrum of gravitational background. The background will cause a daily variation of the noise level. We found that close and rapidly rotating neutron stars would dominate the total signal. We discuss the detectability of such signal.

Speaker: Mr Marcin Kucaba (Institute of Astronomy, University of Zielona Góra)

Slides Kucaba_budapest.pdf

17:50 Efficiency of template banks for highly-eccentric gravitational-wave sources

A large number of predicted waveform templates are used by data analysis of targeted search techniques for merging binary black hole sources based upon matched filtering. Waveforms for inspirals are parametrized by a set of intrinsic physical quantities result an eight-dimensional parameter space. The high dimensionality makes gravitational wave searches, parameter estimation, and modeling prohibitively expensive and computationally unfeasible with most methods. To address these issues, the construction of high-accuracy reduced basis representations that determines a relatively small set of the most relevant waveforms is essential. Our goal has been to develop interpolation techniques in the parameter space of waveforms: with a projection to a lower base, this allows one to significantly reduce the number of templates used and the computational demands for search for signals. Thus the resulted reduction where the eccentricity is about to play the main role will prove to be just as significant as it has been shown in the case of spin. We would like to efficiently compress and accurately represent the space of waveforms for nonprecessing binary black hole inspirals, which constitutes eight-dimensional parameter space. It is expected that the resulted reduction where the eccentricity plays the main role will prove to be just as significant as it has been shown in the case of spin.

Speaker: Mr Dániel Barta (Wigner Research Centre for Physics)

Slides Barta_-_ReducedBasis.pdf Barta_-_ReducedBasis.ppt

14:00 → 18:15 Parallel B: Equation of State

14:00 The crust and the neutron star radius

It will be discussed how the crust-core matching influences the NS radius and the crust thickness within relativistic mean-field nuclear models. A set of models that predict 2$M_\odot$ stars will be considered. It will be proposed an adequate crust-core matching. The inner crust will described in the Thomas-Fermi approximation within the single heavy cluster approach. The effect of considering light cluster will be referred.

Speaker: Constança Providencia (University of Coimbra)

Slides cprovidencia_buda.pdf

14:25 Rotation and stability of neutrons stars with strong phase transtions

Using a recent equation of state (Benic et al., 2015, A&A 577, A40) I will discuss the stability of rotating neutron stars with strong phase transitions (so-called twin family of neutron stars). The existence of an instability region separating the twin families - a direct outcome of the strong phase transition - creates several astrophysical implications that are interesting from the point of view of observational and microphysical aspects of the equation of state.

Speaker: Dr Michał Bejger (N. Copernicus Astronomical Center, PAS)

Slides bejger.pdf

14:50 Core collapse supernova simulations with a new hyperon equation of state compatible with two solar mass neutron star

Supernova explosions are spectacular astronomical events. At the same time, the understanding of the final journey of a massive star after its fuel has been exhausted is a challenging problem. The outcome of it is a core collapse supernova and the residue may take the form of either a neutron star or a black hole. The core collapse supernova explosion mechanism is being investigated over the last five decades. Still, the detailed theory of a successful supernova explosion is beyond our reach. In most core collapse supernova simulations, the shock stalls after traversing a few hundred kilometers. It is not yet understood whether dimension of the problem or microphysics such as equation of state (EoS) of dense matter and neutrino physics is responsible for a successful core collapse supernova explosion. The shock revival by neutrino heating, after hundreds of milliseconds, was investigated in understanding a successful core collapse supernova explosion. On the other hand, novel phases of dense matter such as hyperon, quark or Bose condensates of pions and kaons might be formed just after the bounce of the Fe core. Here I discuss our newly constructed $\Lambda$ hyperon EoS for core-collapse supernova simulations and neutron star mergers. This is the first supernova EoS involving $\Lambda$ hyperons which is compatible with the recently measured 2 M$_{\odot}$ neutron star. I describe the role of strange baryon matter on supernova simulations in GR1D code using our $\Lambda$ hyperon EoS as well as neutrino signal. In this context, I also discuss the metastability of the protoneutron star and its connection to the fate of SN1987A.

Speaker: Prof. Debades Bandyopadhyay (Saha Institute of Nuclear Physics)

Slides deba_buda.pdf

15:15 Pasta phases in core-collapse supernova matter

The pasta phase in core-collapse supernova matter (finite temperatures and fixed proton fractions) is studied within relativistic mean field models. Three different calculations are used for comparison, the Thomas-Fermi (TF), the Coexisting Phases (CP) and the Compressible Liquid Drop (CLD) approximations. The effects of including light clusters in nuclear matter and the densities at which the transitions between pasta configurations and to uniform matter occur are also investigated. The free energy and pressure, in the space of particle number densities and temperatures expected to cover the pasta region, are calculated. Finally, a comparison with a finite temperature Skyrme-Hartree-Fock calculation is drawn.

Speaker: Dr Helena Pais (University of Coimbra)

Slides budapestPais.pdf

15:40 Study of β-stable matter in proto-neutron star: impact by the nuclear symmetry energy at finite temperature

A consistent Hartree-Fock study of the hot, beta-stable baryonic matter of proto-neutron star (PNS) is done based on several choices of the effective (density dependent) nucleon-nucleon interaction, which have been successfully used in different nuclear structure and reaction studies. The equations of state associated with different behaviors of the symmetry energy at supranuclear densities were used to study the npe-muon-neutrino composition of the hot PNS at beta-equilibrium. Both the neutrino-free and neutrino-trapped PNS matters were investigated at different temperature and entropy. The basic properties of PNS like the maximum gravitational mass and radius, the central density, pressure and temperature have been determined at the fixing entropy per baryon and their sensitivity to the nuclear symmetry energy, finite entropy and neutrino trapping are discussed.

Speaker: Ms Hai Tan Ngo (Vinatom,Vietnam/IPNLyon, France)

Slides Compstar-budapest_2015-Haitan.pdf

16:05 Coffee Break

16:35 Thermodynamical behavior of the vector meson extended Polyakov quark meson model

Chiral phase transition is investigated in an $SU(3)_L \times SU(3)_R$ symmetric vector meson extended linear sigma model with additional constituent quarks and Polyakov loops (extended Polyakov quark meson model). The parameterization of the Lagrangian is done at zero temperature in a hybrid approach, where the mesons are treated at tree-level, while the constituent quarks at 1-loop level. The temperature and baryochemical potential dependence of the two assumed scalar condensates and the two Polyakov loop variables are calculated from the hybrid 1-loop level field equations. The order of the phase transition along the $T=0$ and $\mu_B=0$ axes are determined for various parameterization scenarios. We find that in order to have a first order phase transition at $T=0$ as a function of $\mu_B$ a light isoscalar particle is needed. We also calculate the temperature and baryochemcal potential depnedence of the usual thermodynamical quantities such as the pressure and energy density, where we take into account the effects of thermal pion loops as well.

Speaker: Dr Peter Kovacs (Wigner RCP)

Slides pkovacs_CompStar_2015_06_15.pdf

17:00 Constraining supernova equations of state with equilibrium constants from heavy-ion collisions

Cluster formation is a fundamental aspect of the equation of state (EOS) of warm and dense nuclear matter such as can be found in supernovae (SNe). Similar matter can be studied in heavy-ion collisions (HIC). We use the experimental data of Qin et al. [Phys. Rev. Lett. 108, 172701 (2012)] to test calculations of cluster formation and the role of in-medium modifications of cluster properties in SN EOSs. For the comparison between theory and experiment we use chemical equilibrium constants as the main observables. This reduces some of the systematic uncertainties and allows deviations from ideal gas behavior to be identified clearly. In the analysis, we carefully account for the differences between matter in SNe and HICs. We find that, at the lowest densities, the experiment and all theoretical models are consistent with the ideal gas behavior. At higher densities ideal behavior is clearly ruled out and interaction effects have to be considered. The contributions of continuum correlations are of relevance in the virial expansion and remain a difficult problem to solve at higher densities. We conclude that at the densities and temperatures discussed mean-field interactions of nucleons, inclusion of all relevant light clusters, and a suppression mechanism of clusters at high densities have to be incorporated in the SN EOS.

Speaker: Dr Matthias Hempel (Basel University)

Slides hempel_budapest2015.pdf

17:25 Deciphering signatures of EoSs/progenitor models imprinted in GW/neutrino signals emitted from SN cores

In this talk, we present our recently performed 3D fully relativistic long term simulations (Tpb~300-400ms) of gravitational collapse of massive progenitor stars with adopting several modern EoSs of Hempel et al.'12 and of Steiner et al.'13. Through these multiple EoSs and progenitor models, we found more massive progenitor star and softer equation of state lead to more vigorous SASI activity which imprints its characteristic signatures in both gravitational waves (GWs) and neutrino signals. To discuss the possibility of deciphering post bounce hydrodynamic evolution imprinted in GWs, we did our newly developed coherent network analysis and estimated such as the detection limit. We also investigated whether the coherency is found between (1) modulations of GW signals which are associated with SASI activity and of evaluated neutrino count rate; (2) directions of SASI sloshing motion and of prominent neutrino propagation. From these, we can suggest the importance of future coherent observational system between GW and neutrino detectors.

Speaker: Dr Takami Kuroda (University of Basel)

Slides kuroda.pdf

17:50 Analytic structure of nonperturbative quark propagators and meson processes

The analytic structure of certain Ansaetze for quark propagators in the nonperturbative regime of QCD is investigated. When choosing physically motivated parameterization of the momentum-dependent dressed quark mass function M(p^2), with definite analytic structure, it is highly nontrivial to predict and control the analytic structure of the corresponding nonperturbative quark propagator. The issue of the Wick rotation relating the Minkowski-space and Euclidean-space formulations is also highly nontrivial in the nonperturbative case. A propagator form allowing the Wick rotation and enabling equivalent calculations in Minkowski and Euclidean spaces is presented. In spite of its simplicity, this model yields good qualitative and semi-quantitative description of some pseudoscalar meson processes. Extension to finite densities and temperatures is possible.

Speaker: Prof. Dubravko KLABUCAR (Physics Department, PMF, Zagreb University)

Slides KlabucarNewCompStar2015.pdf

Tuesday, 16 June

09:00 → 12:30 Plenary

09:00 From Virgo to ET: the evolution of the GW detectors from the 1st to 3rd generation

The network of Interferometric Gravitational wave detectors is entering in the so-called advanced phase. In few years from now Advanced LIGO and Advanced Virgo are expected to detect the gravitational waves emitted by a binary system of compact stars. The achievements of the initial interferometers, the scientific targets of the advanced and future 3rd generation observatories and the technological evolutions from Virgo to the Einstein Telescope (ET) are briefly discussed.

Speaker: Dr Michele Punturo (INFN and EGO)

Slides NewCompStar2015-Punturo.pptx

10:00 Magnetic, thermal, and rotational evolution of neutron stars

Observations of 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. I review the present theory describing the fully coupled evolution of temperature and magnetic field in neutron stars, and results from numerical simulations, which have been used in population synthesis calculations. By comparing theoretical models to a data sample of 40 sources, we can obtain interesting constraints on the initial magnetic field distribution of neutron stars in the galaxy.

Speaker: Prof. Jose Pons (University of Alicante)

Slides pons_Budapest.pdf

11:00 Coffee Break

11:30 Neutron Stars: Oscillations, Instabilities and Gravitational Waves

We will review recent progress in the study of neutron star seismology, the excitation of rotational instabilities and the associate emission of gravitational waves. We will show the detectability limits of such instabilities for neutron stars emerging from collapse or the aftermath of binary mergers (afterglow). Finally, we will discuss recent progress in the study of neutron stars in alternative theories of gravity.

Speaker: Prof. Kostas Kokkotas (Eberhard Karls University of Tuebingen)

Slides Kokkotas_Budapest.pdf

12:30 → 14:00 Lunch

12:30 Lunch

14:00 → 18:16 Parallel A: Graviational Waves and Neutronstars

14:00 R-mode excitation in accreting neutron stars

Recent X-ray observations have revealed the existence of oscillations during the X-ray bursts of two accreting neutron stars. One possible explanation is that these represent r-mode oscillations. In this talk I explore the r-mode hypothesis, showing that it allows us to place a constraint on the relationship between mass and radius for these two stars. I also discuss what the observations tell us about the strength of dissipative processes within the stars, again adopting the r-mode hypothesis. I conclude by describing the significance of these considerations for gravitational wave searches.

Speaker: Dr Ian Jones (University of Southampton)

Slides dij_compstar_2015.pdf

14:25 Properties of differentially rotating neutron stars

An understanding of differentially rotating relativistic stars is key to many areas of astrophysics, in particular to the emission of gravitational waves. A newly born, proto-neutron star or a compact remnant of neutron stars binary merger are expected to rotate differentially and to be important sources of gravitational radiation. A highly accurate, multidomain spectral code is used in order to construct sequences of general relativistic, differentially rotating neutron stars in axisymmetry and stationarity. The high level of accuracy and stability of the code enable us to study stars with maximal masses and high rotation profiles. We investigate the solution space corresponding to broad ranges of degree of differential rotation and stellar densities. We find various types of configurations, which were not considered in previous work, mainly due to numerical limitations. We study the effects of an equation of state and the degree of differential rotation on properties of rotating neutron stars.

Speaker: Prof. Dorota Rosinska (Institute of Astronomy, University of Zielona Gora)

Slides Rosinska_Compstar2015.pdf

14:50 Forecasting GRBs using gravitational wave detectors

Modern gravitational wave (GW) detectors are hunting for GWs originating from various sources among other from binary neutron star (BNS) coalescence. It is assumed that in some cases it is the coalescence (merging) of such BNS system which is responsible for the creation of gamma-ray bursts (GRBs) - routinely detected by electromagnetic observatories. Since already well before their merging, during the inspiral phase, the binary system emits GWs, analysis groups of GW detectors are performing in-depth search for such events around the time-window of known, already detected GRBs. These joint analysis are very important in increasing the confidence of a possible GW detection. It is widely expected that the first direct detection of GWs will happen in the next few years, and what is a matter of fact that the sensitivity of the next generation of GW detectors will allow us to 'see' a few hundred seconds of inspiral of the binary system before the merge - for specific mass parameter range. From the two above fact, it naturally follows, that one can (should!) turn around the logic and use the GWs emitted during the inspiral phase of a BNS coalescence process to predict, in advance the time and sky location of a GRB and set up constraints on the physical parameters of the system. There exists no such prediction algorithm, as of today. Despite the fact that it is not yet feasible to use this new method with the current GW detectors, it will be of utmost importance in the late-Advanced LIGO/Virgo era and definitely for Einstein Telescope. The very goal of the research presented in this talk is to develop the above described zero-latency, BNS coalescence 'forecasting' method and set up and organize the associated alert system to be used by next generation of gravitational wave detectors and collaborating EM observatories.

Speaker: Dr Gergely Debreczeni (Wigner RCP)

Slides DebreczeniG_2015.06.16_-_CompStar.pdf

15:15 Models of differentially rotating Strange Quark Stars in General Relativity

Strange quark stars are considered as a possible alternative to neutron stars as compact objects. We present first fully relativistic calculations of differentially rotating strange quark stars for broad ranges of stellar masses and the degree of differential rotation. A newly born, hot neutron star (or a strange star) formed in a supernova explosion is supposed to rotate differentially. Using a highly accurate, relativistic code we calculate main properties (e.g. allowed masses, radii, the stability parameters) of rigidly and differentially rotating strange quark stars. We show that the rotation may cause a significant increase of maximum allowed mass of strange quark star, much larger than in the case of neutron stars. A compact star stabilized by differential rotation could be an important source of gravitational waves.

Speaker: Ms Magdalena Szkudlarek (Kepler Institute of Astronomy University of Zielona Gora)

Slides Szkudlarek_CompStar2015.pdf

15:40 On the tidal Love numbers of rotating neutron stars

Tidal Love numbers carry valuable information on the inner structure of a neutron star, and on its equation of state. This information could be extracted, by IInd and IIIrd generation gravitational wave detectors, from the gravitational wave signal emitted by coalescing neutron star-neutron star binaries. Up to now, the theoretical modelling and computation of Love numbers has been limited to static, spherically symmetric objects. We want to compute the Love numbers of rotating neutron stars. To this aim, using a perturbative approach, we have studied the solutions of Einstein's equations describing a spinning compact object distorted by an axisymmetric tidal field. We have considered black hole solutions up to second order in the rotation rate, and neutron star solutions up to first order in the rotation rate, finding out the corrections to Love numbers due to rotation. Our preliminary results suggest that in the case of neutron stars, rotation may give a significant contribution to the tidal Love numbers, and to the mass quadrupole.

Speaker: Dr Leonardo Gualtieri (Dipartimento di Fisica, "Sapienza" Università di Roma)

Slides Gualtieri_CompStar2015.pdf

16:05 Coffee Break

16:35 A post-TOV formalism for relativistic stars

In this talk we discuss a parametrised formalism for describing relativistic stars beyond General Relativity, without committing to any particular modified theory of gravity. We show how the deviations from GR are reflected on the stellar mass-radius and demonstrate the equivalence between this "post-TOV" formalism and an effective GR description.

Speaker: Dr Kostas Glampedakis (University of Murcia)

Slides KoctasGlampedakis_Budapest_2015.pdf

17:00 A realistic model of a neutron star in a modified theory of gravity

The well-known serious difficulties in numerical investigation of realistic models of neutron stars (NS) in the modified theories of gravity [1] are surmounted on a general basis. Developing the recent results of the author [2-4] we present a realistic model of static spherically symmetric NS with AMP1 EOS using the correct boundary conditions at the center, at the edge, and at the cosmological horizon of the de Sitter like Universe with only one such star. The critical step is the introduction of new field variable for the scalar degree of freedom which we call “the dark scalar”. The maximal mass or the NS turns to be around 2.7 solar masses and depends on the mass of the dark scalar. We investigate for the first time this dependence, as well as the influence of the dark scalar on the gravitational field inside the NS and its exponentially decreasing dark halo outside the star. The dark halo may give some 15 % of the total mass of the NS. The behavior of the newly introduced pressure and mass density of the dark matter and dark energy are also studied and discussed. References: 1. E. Berti et al, Testing General Relativity with Present and Future Astrophysical Observations, TOPICAL REVIEW, Class.Quant. Grav. (2015); arXiv:1501.07274. 2. P.P. Fiziev, PRD 87, 0044053 (2013); arXiv:1209.2695. 3. P.P. Fiziev, PoS (FFP14) 080 (1914); arXiv:1402.2813, arXiv:1411.0242. 4. P.P. Fiziev, K. Marinov, BAJ, 23, (2015); arXiv:1412.3015.

Speaker: Dr Plamen Fiziev (Sofia University Foundation for Theoretical Physics and Astrophysics)

Slides Fiziev_16_06_2015_new.pdf

17:25 Can Massive Kaluza–Klein Stars exist?

Theoretical descriptions of compact stars have been extensively studied long time ago. The description of these extreme objects of the Universe are required to handle both the high-energy particle/nuclear physics and the gravitational theory in parallel. A possible theoretical phenomena based on the Kaluza –Klein geometrization of interactions also provides a simply model for the compact objects, however the obtained masses are well below, that we can measured by pulsars. Here, we would like to investigate whether the recent and proposed measurements are supporting the existence of a compactified extra dimensions.

Speaker: Ms Szilvia Karsai (Eötvös University Budapest)

Slides Sz_Karsai_CompStar2015Bp.pdf

17:50 -

14:00 → 18:15 Parallel B: Equation of State

14:00 FRG Approach to Nuclear Matter in Extreme Conditions

Functional renormalization group (FRG) is an exact method for taking into account the effect of quantum fluctuations in the effective action of the system. The FRG method applied to effective theories of nuclear matter yields equation of state witch incorporates quantum fluctuations of the fields. Using the local potential approximation the equation of state for Walecka-type models of nuclear matter under extreme conditions is determined. These models are tested by solving the corresponding Tollman-Oppenheimer-Volkov (TOV) equations and investigating the properties (mass and radius) of the corresponding compact star models.

Speaker: Mr Peter Pósfay (Eötvös Lóránd University)

Slides Posfay_Peter_2015_compsta_conference.pdf

14:25 An Advanced Relativistic Mean-Field Theory for Dense Nuclear Matter

Modern and accurate observations of compact stars are invaluable sources of very important information about dense nuclear matter. One of the biggest breakthroughs in this field is definitely an experimental confirmation of the existence of very massive pulsars that brought new and very powerful constraints on all model descriptions. Our aim is to develop a relativistic energy density functional in the framework of the density dependent mean-field theory (MFT), which could be applied to dense nuclear matter as well as to compact star physics. Since a basic MFT does not take into account an exact momentum dependence and operates on the Hartree level only, we derived an advanced MFT that addresses these issues. In the first step, we extracted a momentum corrected parametrizations from the microscopic Dirac-Brueckner-Hartree-Fock (DBHF) data using our 2-parametric class of density functions and calculated properties of symmetric and asymmetric nuclear matter. In the second step, we created a model that reflects and properly comprises the Fock (exchange) part of the energy density of nuclear matter. This was done by mapping the Fock contributions, defined by the linear Dirac-Hartree-Fock theory, onto a density dependent MFT in a closed parameter-free form, expressed as a density functional. Preliminary calculations show promising improvements of results for the dense nuclear matter.

Speaker: Dr Kristian Petrik (Institute of Physics, Slovak Academy of Sciences)

Slides Prezentacia_2015_compstar.pdf

14:50 RMF model with scaled hadron masses and coupling constants and the hyperon puzzle

The equation of state of cold baryonic matter is studied within a relativistic mean-field model with hadron masses and coupling constants depending on the scalar field. All hadron masses undergo a universal scaling, whereas the coupling constants can scale differently. The proper choice of the scaling function allows to control stiffness of the equation of state in different energy range. The appearance of hyperons in dense neutron star interiors is accounted for. However the equation of state remains sufficiently stiff if a reduction of the $\phi$ meson mass is included. Our equation of state matches well the constraints known from analyses of the astrophysical data and the particle production in heavy-ion collisions.

Speaker: Dr Evgeni Kolomeitsev (Matej Bel University)

Slides Kolomeitsev-Compstar15.ppt

15:15 Unified equations of state for neutron stars within the energy-density functional theory and neutron-star structure

In this talk, a set of unified equations of state (EoSs) of neutron-star matter calculated within the nuclear energy-density functional theory, and based on generalised Skyrme energy-density functionals developed by the Brussels-Montreal collaboration, will be presented. The structure of neutron stars constructed with these EoSs will be discussed in connection with both recent astrophysical observations and nuclear-matter parameters, for both accreting and non-accreting neutron stars.

Speaker: Dr Anthea Francesca Fantina (Institut d'Astronomie et d'Astrophysique, Université Libre de Bruxelles)

Slides Fantina_NewCompStar2015.pdf

15:40 Supporting the existence of the QCD critical point by compact star observations

In order to prove the existence of a critical end point (CEP) in the QCD phase diagram it is sufficient to demonstrate that at zero temperature $T=0$ a first order phase transition exists as a function of the baryochemical potential $\mu$, since it is established knowledge from ab-initio lattice QCD simulations that at $\mu=0$ the transition on the temperature axis is a crossover. We present the argument that the observation of a gap in the mass-radius relationship for compact stars which proves the existence of a so-called third family (aka "mass twins") will imply that the $T=0$ equation of state of compact star matter exhibits a strong first order transition with a latent heat that satisfies $\Delta\epsilon/\epsilon_c >0.6$ [Alford et al., arxiv:1302.4732]. Since such a strong first order transition under compact star conditions will remain first order when going to symmetric matter, the observation of a disconnected branch (third family) of compact stars in the mass-radius diagram proves the existence of a CEP in QCD. For the equation of state of the twins the quark matter description is based on a QCD-motivated chiral approach with higher-order quark interactions in the Dirac scalar and vector coupling channels. For hadronic matter we select a relativistic mean-filed equation of state with density-dependent couplings. Since the nucleons are treated in the quasi-particle framework, an excluded volume has been included for the nuclear equation of state at super-saturation density that takes into account the finite size of the nucleons. Furthermore we show results of a Bayesian analysis (BA) using disjunct M-R constraints for extracting probability measures for cold, dense matter equations of state. In particular this study reveals that measuring radii of the neutron star twins has the potential to support the existence of a first order phase transition for compact star matter.

Speaker: Dr David Alvarez-Castillo (Joint Institute for Nuclear Research)

Slides Alvarez_-_CompStar_-_2015.pdf

16:05 Coffee Break

16:35 Constraining neutron star properties with perturbative QCD

I will describe what is currently known about the behavior of the Equation of State (EoS) of cold and dense quark matter based on first principles calculations utilizing perturbation theory in the deconfined phase of QCD. In addition, I will argue that by combining this information with known results on the EoS of low-density nuclear matter, it is possible to very efficiently constrain the thermodynamic properties of neutron star matter at all densities. Finally, the implications of these studies on neutron star properties as well as the future prospects of decreasing the current level of uncertainty in the calculations will both be discussed in detail.

Speaker: Dr Aleksi Vuorinen (University of Helsinki)

Slides vuorinen.pptx

17:00 Hyperonic three-body forces and consequences for neutron stars

We construct two-meson exchange three-baryon potentials between two nucleons and one hyperon (NNY). Our NNY potentials are built in order to be consistent with the most recent version of the two-body nucleon- hyperon (NY) potential of the Juelich group. In particular, we focus on the NNΛ and NNΣ forces since the Λ and Σ− are the first hyperons expected to appear in microscopic calculations of neutron star matter. We provide the explicit expressions for the various potentials in r-space in such a way that they can be used both in finite hypernuclei as well as hyperonic matter calculations. We finally discuss several calculations of hyperonic matter, based on the Brueckner–Hartree–Fock approach, including the effect of the hyperonic three-body forces. These results suggest that at high densities the total contribution of the NNY force is repulsive making the resulting equation of state (EoS) stiffer, as required from neutron star mass observations.

Speaker: Dr Isaac Vidana (University of Coimbra)

Slides compstar2015_vidana.pdf

17:25 Properties of neutron-star crusts with accurately calibrated nuclear energy density functionals

Observations from ground- and space-based instruments have lead to the discovery of remarkable astrophysical phenomena that are thought to be intimately related to the physics of neutron-star crusts like pulsar sudden spin-ups (so called “glitches”), quasi-periodic oscillations in the giant flares from soft gamma-ray repeaters, X-ray bursts and superbursts, or the cooling of quasi-persistent soft X-ray transients. The crust composition is also essential to evaluate the possible contribution of neutron stars to the galactic enrichment in the so-called r-process nuclei, whose origin remains one of the major mysteries in astrophysics. During this talk, we will present the latest developments of the Brussels-Montreal collaboration in the modelling of neutron-star crusts using accurately calibrated nuclear energy density functionals based on generalized Skyrme effective interactions.

Speaker: Dr Nicolas Chamel (Université Libre de Bruxelles)

Slides chamel-compstar-2015.pdf

17:50 Vortex Creep Against Toroidal Flux Lines and Implications for Pulsar Glitches and Neutron Star Structure

As theoretical calculations and recent simulations indicate, neutron stars must have a stronger toroidal field component in the outer core which surrounds the poloidal field. Then, this toroidal field in the form of flux lines will offer pinning sites for vortex lines similar to the conditions in the inner crust. As we have shown, the moment of inertia of the corresponding region can be larger than that of the crust depending on the radial extension of the toroidal flux. Furthermore, we found that the response of the toroidal flux line region to a glitch is exponential relaxation with timescales of the order of several days to months fitting the postglitch observations. Due to the contribution of toroidal flux region, angular momentum constraint for the glitches changes and our findings can resolve entrainment crisis for large glitches.

Speaker: Mr Erbil GÜGERCINOGLU (Istanbul University Astronomy and Space Sciences Department)

Slides Erbil-Vortex_Creep_Against_Toroidal_Flux_Lines_and_Implications_for_Pulsar_Glitches_and_Neutron_Star_Structure.pptx

Wednesday, 17 June

09:00 → 12:30 Plenary

09:00 Nucleosynthesis of heavy elements in supernovae and neutron star mergers

We will discuss new results on nucleosynthesis in core-collapse supernovae and neutrino-driven winds that produce elements up to silver. Because the synthesis of these elements occurs closer to stability, in the near future, the nuclear physics uncertainties will be reduced by experiments. This will uniquely allow us to combine observations and nucleosynthesis calculations to constrain the astrophysical conditions in neutrino-driven winds and thus gain new insights about core-collapse supernovae. In addition, we will discuss the production of all r-process elements (from the first to the third peak) in neutron star mergers. The radioactive decay of neutron-rich nuclei triggers a electromagnetic signal in mergers known as kilonova. This was potentially observed after a short gamma ray burst, associated with a neutron star merger. Nucleosynthesis in mergers takes place far away from stability and our sensitivity studies show the importance of, in particular, nuclear masses and fission properties.

Speaker: Almudena Arcones (TU Darmstadt)

Slides arcones.pdf

10:00 Constraining neutron stars EoS with gravitational wave observations

Gravitational waves emitted by neutron stars in various astrophysical processes, have been shown to carry the imprint of the equation of state (EoS) of matter in the star inner core. I will discuss which are the perspectives of constraining the EoS of dense matter with the Advanced Virgo/LIGO detectors, expected to become operational within a year, and with the next generation of ground-based, interferometric detectors ET.

Speaker: Prof. Valeria Ferrari (Dipartimento di Fisica, Sapienza Universita' di Roma)

Slides ferrari.pdf

11:00 Coffee Break

11:30 From holography towards real-world nuclear matter

QCD is notoriously difficult to solve at nonzero baryon density, and most models or effective theories of dense quark or nuclear matter are restricted to a particular density regime and/or a particular form of matter. I will discuss the question whether holographic methods can provide a realistic strong-coupling description of dense matter. In particular, I will ask the question whether the holographic Sakai-Sugimoto model fulfills two basic requirements of real-world cold and dense matter, a first-order onset of nuclear matter and a chiral phase transition at high density to quark matter. Such a model would be extremely useful for astrophysical applications because it would provide a single equation of state for all densities relevant in a compact star.

Speaker: Andreas Schmitt (TU Wien)

Slides schmitt.pdf

12:00 QCD Thermodynamics from Effective Field Theories

I will give a brief overview on thermodynamics and the phse structure of QCD including recent developments from lattice QCD and effective theory approach. The following selected issues will be discussed; interplay between confinement and dynamical chiral symmetry breaking, nuclear matter near chiral symmetry restoration, correlations between light and heavy flavors.

Speaker: Dr Chihiro Sasaki (FIAS)

Slides ChihiroSasaki_budapest.pdf

12:30 → 14:00 Lunch

12:30 Lunch

14:00 → 15:00 Plenary

14:00 The Equation of State of Neutron Star Matter

I review the main features of the Equation of State of Neutron Star Matter, including strange and quark matter degrees of freedom. Results obtained in several different theoretical frameworks will be discussed, with special emphasys on the Bruckner-Hartree-Fock approach.

Speaker: Dr Fiorella Burgio (INFN Catania)

Slides Fiorella_Talk_Budapest.pdf

15:00 → 15:35 Coffee Break

15:35 → 19:25 Management Committee Meeting COST Action MP1304 - Closed meeting

15:35 Welcome & Adoption of the agenda

15:45 Approval of teh minutes of the last meeting

15:55 Update from the Action Chair

16:25 Update from the Gender Coordinator

16:35 Update from the Outreach Coordinator

16:50 Update from the Synergy Agents

17:20 Update from the Working Group Leaders

17:50 Future Planning

18:10 Miscellanea & Location and date of the next meeting

18:20 Location and date of the next meeting

18:30 Summary & Closing

16:00 → 17:00 Tudománynépszerüsítő előadás: Outreach Talk (in Hungarian)

Convener: Prof. Gábor Papp (Eötvös University)

16:00 A halott csillagok élete -- avagy van-e élet a fekete lyuk előtt

Speaker: Prof. Gábor Papp (Eötvös University)

Thursday, 18 June

09:00 → 12:30 Plenary

09:00 Constraining the neutron star equation of state with future telescopes

Astronomers observe neutron stars in many guises. We see pulsars that emit regular radio, X-ray or gamma-ray signals. We observe systems that emit X-rays as they accrete matter from a binary companion. The observations allow us – at least in principle – to probe a regime of physics that can never be reached in terrestrial laboratories, allowing us to constrain the equation of state at supranuclear densities. However, neutron stars are hands-off laboratories. We can only extract the fundamental physics indirectly, by matching our theories to observed behaviour. Given the variety of observed phenomena and the fact that neutron stars come in many guises, this is a serious challenge. In this talk I will summarise the current state-of-the-art of this area, and describe how a revolutionary generation of telescopes may lead to a breakthrough in our understanding of matter under extreme conditions.

Speaker: Prof. Nils Andersson (University of Southampton)

Slides Andersson.pdf

10:00 Pulsars from optical to gamma-rays

For most of the known pulsars their emission is powered by the loss of the their rotational energy. The noncoherent, nonthermal emission has been detected form optical to TeV gamma-rays in >100 pulsars. In a few pulsars we also can see thermal radiation from the neutron star surface/atmosphere. I will review the properties of both components including their efficiencies, dependence of radiation properties on pulsar age and spin-down power, connection between the pulsar and pulsar-wind nebula emission. I will describe the most interesting recent findings.

Speaker: Prof. Oleg Kargaltsev (The George Washington University)

Slides kargaltsev_NewCompStar2015short.pptx

11:00 Coffee Break

11:30 Recent results on magnetars

Soft Gamma-ray Repeaters (SGRs) and Anomalous X-ray pulsars (AXPs) are peculiar X-ray sources which are believed to be magnetars: ultra-magnetized neutron stars with surface field in excess of 10^14 G, i.e. well above the QED threshold. For this reason their study has far reaching implications for several fields of physics and astrophysics. After summarizing the properties of these sources and the evidence that they consist of highly magnetized neutron stars, I will present the results of recent observations focusing in particular on the discovery of magnetars with surprisingly small period derivatives.

Speaker: Prof. Sandro Mereghetti (INAF, IASF-MILANO)

Slides MEREGHETTI_COMPSTAR2015.pdf

12:00 Hydrodynamic and magnetic activity in neutron stars

Hydrodynamic and magnetic activity in neutron stars

Speaker: Prof. Andrew Melatos (University of Melbourne)

Slides 2015Budapest-v3-Melatos.pdf

12:30 → 14:00 Lunch

12:30 Lunch

14:00 → 17:50 Parallel A: Magnetars and Neutronstars

14:00 Modelling Strongly Magnetized Neutron Stars in General Relativity.

The morphology of the strong magnetic fields hosted by neutron stars plays a key role in establishing and governing the physics and the observational properties of these extreme astrophysical objects. Hence an accurate description of magnetic fields in neutron stars provides a necessary ingredient to develop realistic physical models able to shed light on the phenomenology of these compact objects. In particular, recent observations of AXPs and SGRs, support the idea of a twisted magnetosphere, and complex geometry that goes beyond the simple dipole often used in the literature. I will present the results of a comprehensive numerical study of magnetic configurations in NSs, derived in the full GR regime, taking into account different magnetic field geometries (including the mixed poloidal-toroidal case) that arise from different choices of the current distributions located both in core and in peripheral region inside the star, but also outside in the near magnetosphere. These will be analysed in the context of their stability and possible origin. The role of magnetic field in young objects and the relative importance of EM to GW emission will be also discussed, with a particular focus on GRBs.

Speaker: Mr Antonio Graziano Pili (Università degli Studi di Firenze)

Slides Pili.pdf

14:25 Magnetic Field Evolution in Superconducting Neutron Stars

The presence of superconducting and superfluid components in the core of mature neutron stars calls for the rethinking of a number of key magnetohydrodynamical notions like resistivity, the induction equation, magnetic energy and flux-freezing. Using a multi-fluid magnetohydrodynamics formalism, we investigate how the magnetic field evolution is modified when neutron star matter is composed of superfluid neutrons, type-II superconducting protons and relativistic electrons. As an application of this framework, we derive an induction equation where the resistive coupling originates from the mutual friction between the electrons and the vortex/fluxtube arrays of the neutron and proton condensates. The resulting induction equation allows the identification of two timescales that are significantly different from those of standard magnetohydrodynamics and could have important astrophysical implications. The talk is based on recent work, which is discussed in more detail in arXiv:1505.00124.

Speaker: Ms Vanessa Graber (University of Southampton)

Slides Budapest_VGraber.pdf

14:50 Probing superfluid properties of magnetars with magneto-elastic oscillations

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≲150Hz and resonantly excited high-frequency QPOs (f>500Hz), 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)

Slides Gabler_CompStar2015.pdf

15:15 Transport coefficients in superfluid matter in neutron stars

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 and the gap. 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 superfluid core of the neutron stars. 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)

Slides Tolos_CompStar2015.pdf

15:40 Coffee Break

16:10 Magnetar formation from the merger of binary neutron stars

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

Speaker: Bruno Giacomazzo (University of Trento)

Slides Giacomazzo_Compstar_June_2015.pdf

16:35 Magneto-thermal evolution of high-B neutron stars subject to core field expulsion

State-of-the-art 2D simulations of coupled magnetic and temperature evolution have shown us that we can explain different neutron star (NS) classes by varying only magnetic field strength and geometry at birth. In this work we address evolutionary differences that arise as a consequence of including the physics driving magnetic field evolution in the NS core. Forcing in the core arises due to the interactions between superfluid neutron vortices and the entrained magnetic flux-tubes. We describe, for the first time, the results from self-consistent magneto-thermal simulations considering not only the effects of Hall-driven field dissipation in the crust, but adding a complete set of proposed driving forces in the core. We emphasize how each of these theorized processes drive magnetic evolution and affect observables, and show that when all forces are considered vectorially, the net expulsion rate is negligible, and will have no observable effect in the crust on megayear timescales.

Speaker: Dr Justin Elfritz (Anton Pannekoek Institute, University of Amsterdam)

Slides Elfritz_NSC_final.pdf

17:00 The Abnormal Glitch Signature of PSR J1119-6127 and the Vortex Creep Model

Standard glitches are characterized by a positive step in angular velocity and a negative step in the spin-down rate of the pulsar. There are no glitch-associated changes in the electromagnetic signature of rotation- powered pulsars in all cases so far. For the first time, in the last glitch of PSR J1119- 6127, there is clear evidence for changing emission properties coincident with the glitch. This glitch is also unusual in its signature. Further, the absolute value of the spin-down rate actually decreases in the long term. This is in contrast to usual glitch behaviour. In this paper we extend the vortex creep model in order to take into account these peculiarities. We propose that a starquake with crustal plate movement towards the rotational poles of the star induces inward vortex motion which causes the unusual glitch signature. The component of the magnetic field perpendicular to the rotation axis will decrease, giving rise to a permanent change in the pulsar external torque.

Speaker: Mr Onur Akbal (Sabanci University)

Slides Onur_Akbal_CompStar2015.pdf

17:25 Cancelled Talk

14:00 → 17:50 Parallel B: Gamma Ray Bursts and Nuclear Matter

14:00 The X-ray outburst of the Galactic Centre magnetar during the first 1.5 year

In 2013 April a new magnetar, SGR 1745−2900, was discovered as it entered an outburst at only 2.4 arcsec angular distance from Sagittarius A∗, the supermassive black hole at the centre of the Milky Way. The new source was detected both in the radio and X-ray bands, with a peak X-ray luminosity L_X ∼ 5 × 10^{35} erg s^{−1}. I will present the results of the long-term Chandra (25 observations) and XMM–Newton (eight observations) X-ray monitoring campaign of SGR 1745−2900 from the onset of the outburst in 2013 April until 2014 September. This unprecedented data set has unveiled an extremely slow flux decay for the source, and a rather inefficient surface cooling. I will show how starquake-induced crustal cooling models alone have difficulty in explaining the prolonged high luminosity of the source for the first ∼200 days of its outburst. Additional heating of the star surface from currents flowing in a twisted magnetic bundle is probably playing an important role in the outburst evolution.

Speaker: Mr Francesco Coti Zelati (Anton Pannekoek Institute for Astronomy, University of Amsterdam)

Slides Francesco_CotiZelati.pdf

14:25 Vortex motion in neutron star crusts and pulsar glitches

Pulsar glitches, i.e. sudden jumps in the frequency of spinning down pulsars, are thought to be the direct manifestation of a superfluid component in the pulsar interior. The exact mechanisms that gives rise to these phenomena has, however, remained a mystery for over 40 years. The wealth of data that is now available suggests that glitches may be the consequence of the superfluid being in a self-organised-critical state and releasing angular momentum via discrete vortex avalanches, that give rise to the observed glitch. This expectation has been borne out by quantum mechanical simulations of pinned vortices in a spinning down container, but doubts remain as to the applicability of these results to a neutron star, given that simulations cannot probe the realistic regime in which vortices are very far apart and separated by up to 10^10 pinning sites. In this talk I will study the problem of how far a vortex can travel in a realistic neutron star crust, and whether vortex-vortex interactions are possible. I will show that there is a large region of parameter space in which vortex avalanches are possible and I will review some of the results from quantum mechanical simulations being carried out in Melbourne.

Speaker: Dr Brynmor Haskell (University of Melbourne)

Slides HaskellBudapest.pdf

14:50 Glitches and anti-glitches in accreting pulsars: expected properties and observability

Glitches have been observed in isolated pulsars, while a clear detection in accretion-powered X-ray pulsars is still lacking. We use the "snowplow" model for pulsar glitches of Pizzochero (2011) and starquake models to determine for the first time the expected properties of glitches in accreting pulsars and their observability. We also investigate the possibility that anti-glitches occur in accreting pulsars which show accretion-induced long-term spin-up. We find that glitches caused by quakes in a slow accreting neutron star are very rare and their detection extremely unlikely. On the contrary, glitches and anti-glitches caused by a transfer of angular momentum between the superfluid neutron vortices and the non-superfluid component may take place in accreting pulsars more often. We calculate that the maximum jump in angular velocity of an anti-glitch is expected to be about 1E-5 - 1E-4 rad/s. We also find that both glitches and anti-glitches in accreting pulsars are expected to have long rise and recovery time scales compared to isolated glitching pulsars. We find that, among accreting pulsars, GX 1+4 is the best candidate for the detection of glitches with currently operating X-ray instruments and future missions such as the Large Observatory for X-ray Timing (LOFT).

Speaker: Dr Lorenzo Ducci (University of Tuebingen)

Slides ld_budapest.pdf

15:15 LOFAR's view on mode-switching pulsar B0943+10

PSR B0943+10 is one of the best examples of the rare class of mode-switching pulsars. Unlike most of the pulsar population, PSR B0943+10 has two stable modes of radio emission, each with its own distinct radio profile morphology and sinlge-pulse behaviour. The pulsar switches between "Bright" and "Quiet" modes once every few hours and the transition takes less than a few stellar rotations. The switch in the radio modes is also accompanied by changes in the X-ray emission mode (Hermsen et al. 2013) indicating that mode switching is a rapid and global transformation of the magnetosphere and its broadband emission. The exact nature of this transformation, however, is still far from being well understood. With the goal of better illuminating the difference between the two modes, we carried out sensitive, multi-hour LOFAR observations below 100 MHz, where the frequency-dependent changes in the pulse-profile morphology are the largest, and effects too subtle to see at higher frequencies become readily evident. We present detailed review of the pulsar's magnetospheric geometry, describe the frequency evolution of the average profile and constrain the emission regions in both modes within the frame of radius-to-frequency mapping theory. We also investigate the gradual changes in the shape of the average profile within a single mode instance. Finally, we explore drifting subpulses in the Bright mode and give a geometrical explanation for the discovered frequency-dependent delay in the drift phase.

Speaker: Dr Anna Bilous (Radboud University Nijmegen)

Slides Bilous_BP.pdf

15:40 Coffee Break

16:10 Discovery of a narrow, phase-dependent feature in the X-ray spectrum of RX J0720.4-3125

In this talk I would like to report the discovery of a narrow phase-dependent absorption feature in the X-ray spectrum of the nearby X-ray Dim Isolated Neutron Star RX J0720.4-3125. This feature was discovered performing a detailed phase-resolved spectral analysis using XMM-Newton observations which cover 12 years. The line seems to be stable in time over this timespan and is present in 20% of the pulsar rotation. Because of its narrow width and its strong dependency on the rotational phase, the spectral line is probably due to proton cyclotron absorption in a ~10^14 G confined magnetic structure (with a field strength about 7 times the dipolar field of this pulsar).

Speaker: Ms Alice Borghese (Anton Pannekoek Institute for Astronomy)

Slides Budapest3.pdf

16:35 The supernova remnant G284.3-1.8 and the X-ray binary 1FGL J1018.6-5856

It is extremely rare when a binary is found to be associated with supernova remnant. It is also rare when a high-mass binary is bright in gamma-rays. SNR G284.3-1.8 appears to be a unique remnant hosting such a binary. We present results from Chandra and XMM-Newton observations of the SNR and the binary. G284.3-1.8 has asymmetrically distributed Mg-rich ejecta, which has only been observed in one other remnant. It also appears to be interacting with a molecular cloud in the north. It is clear that the SN progenitor was a massive star, but the unknown nature of the compact object complicates the binary evolution modeling. We will report the variability and spectral analysis for the binary X-ray emission and discuss the constraints our results place on the SNR progenitor system and the high-mass binary evolution scenarios.

Speaker: Dr Blagoy Rangelov (The George Washington University)

Slides G284_J1018v2.pdf G284_J1018v2.ppt

17:00 Comparing different models of pulsar timing noise

Variability in the arrival times of pulsars, often collectively known as timing noise, poses a significant opportunity to learn about the physics of neutron stars. The diversity of observed timing noise is matched by the number of the models attempting to explain the phenomenon, but no single model can claim to provide a complete explanation. Recent results in the literature suggest that periodic, or at least quasi-periodic variations may explain some of the observed timing noise. I will present work studying periodic variations in PSR B1828-11, a pulsar that has been used to verify two leading models capable of explaining the periodic variations: magnetospheric switching and precession. I will demonstrate how we can build a statistical model to make inferences about these models, and do a Bayesian model comparison to quantify which the data prefers.

Speaker: Mr Gregory Ashton (University of Southamton)

Slides GregAshton_NewCompStarBudapest.pdf

17:25 Study of low-density nuclear matter by quantum molecular dynamics simulations: Role of symmetry energy

We study the structure of nuclear matter at sub-saturation densties by quantum molecular dyanamics simulations. In particular, we investigate the role of nuclear symmetry energy and its slope on the properties of pasta phases.

Speaker: Dr Rana Nandi (FIAS)

Slides md.pdf

18:15 → 18:50 Travel to the Conference Dinner site

Bus starts from Hotel Mercure Buda

19:00 → 22:00 Conference Dinner

Friday, 19 June

09:00 → 12:00 Plenary

09:00 Gamma-ray bursts and magnetars: observational signatures and predictions

Newly-born millisecond magnetars are competing with black holes as source of the gamma-ray burst (GRB) power, mainly with their rotational energy reservoir. They may be formed both in the core-collapse of massive stars, and in the merger of neutron star or white dwarf binaries, or in the accretion-induced collapse of a white dwarf, being thus a plausible progenitor for long and short GRBs, respectively. In ten years of activity, Swift has provided compelling observational evidences supporting the magnetar central engine, as the presence of a plateau phase in the X-ray light curve, the extended emission in SGRBs and the precursor and flaring activity. We review the major observational evidences for the possible presence of a newly-born magnetar as the central engine for both long and short GRBs. We then discuss about the possibility that all GRBs are powered by magnetars, and we propose a unification scheme that accommodates both magnetars and black holes, connected to the different properties and energetics of GRBs.

Speaker: Dr Maria Grazia Bernardini (INAF - Osservatorio Astronomico di Brera)

Slides Bernardini_CompStar2015.pdf

10:00 Glitches, Neutron Star Structure and External Torques: New Developments, New Perspectives

Recent pulsar glitch observations indicating changing external torques, and developments in theory have opened a new perspective on neutron star structure and dynamics. Triggers and amplifiers of pulsar glitches; the roles of superfluidity and crust rigidity; the new perspectives required by the effects of Bloch entrainment; the coupling of sudden changes in internal and external torques and structure and the roles of the magnetic fields will be addressed in the pulsar context with extension to magnetars.

Speaker: Prof. M. Ali Alpar (Sabanci University)

Slides Alpar_CompStar2015.pptx

11:00 Coffee Break

11:30 Summary of the NewCompStar 2015 Annual Conference

Speaker: Dr Gergely Gábor Barnaföldi (Wigner RCP RMI of the Hungarian Academy of Sciences)

Slides BarnafoldiGG_NewCompStar_Summary_2015v3.pdf

12:00 → 12:10 Closing

Convener: Dr Gergely Gábor Barnaföldi (Wigner RCP RMI of the Hungarian Academy of Sciences)

12:00 Closing Remarks

12:10 → 13:40 Lunch

12:10 Lunch