Location: Park 1.23

R1 - Monday 14:00-15:40 (Vanessa Graber)

Properties of matter in the core of neutron stars


Milva Gabriela Orsaria (Grupo de Gravitación, Astrofísica y Cosmología, Facultad de Ciencias Astronómicas y Geofísicas)

The study of neutron stars establishes a direct connection between astronomy and nuclear and particle physics, allowing a better understanding of the behavior of matter under conditions that are difficult to achieve in the laboratory. In particular, the neutron stars of 2 solar masses provide very important restrictions on the high density nuclear matter and its associated state equation (EoS), which is still essentially unknown. Moreover, the recent direct observation of the gravitational wave event GW170817 and its GRB170817A signal has opened a new window to study neutron stars, imposing new restrictions on such EoS. At the group of Gravitation, Astrophysics and Cosmology, we study the existence of a possible hadron-quark phase transition in the central regions of neutron stars and the changes it produces on the gravitational modes frequencies emitted by these stars. In addition, we study the influence of strong magnetic fields in hybrid stars, composed by hadrons and a pure quark matter core, and analyse their structure and stability as well as some possible evolution channels due to the magnetic field decay. In this talk, I will present the new theoretical results obtained and I will discuss about the dense matter composing neutron stars, the determination of the EoS and some of the restrictions imposed by astrophysical observations on these fascinating compact objects.

Dark matter and bubble nucleation in old neutron stars


Maria Angeles Pérez García (Fundamental Physics, University of Salamanca)

We study the probability for nucleation of quark matter droplets in the dense cold cores of old neutron stars induced by the presence of a self-annihilating dark matter component, $chi$. Using a parameterized form of the equation of state for hadronic and quark phases of ordinary matter, we explore the thermodynamical conditions under which droplet formation is facilitated by energy injection from $chi$ self-annihilations. We obtain the droplet nucleation time as a function of the dark matter candidate mass, $m_chi$. We discuss further observational consequences.

The results of this work appear on A. Herrero, M. Angeles P’erez-Garc’ia, J. Silk, C. Albertus, arXiv and have been accepted for publication in Phys. Rev. D

Density Dependence of B-parameter of anisotropic Compact object with Quark Matter


Pradip Kumar Chattopadhyay Chattopadhyay (Physics, Coochbehar Panchanan Barma University)

A class of relativistic solutions for compact cold objects with strange matter in a pseudo-spheroidal space-time is presented here. Considering strange matter equation of state namely, $p = frac{1}{3}(rho-4B)$, where $rho$, $p$ and $B$ are energy density, pressure and MIT Bag parameter respectively, stellar models are obtained. Stellar models are explored where the Bag parameter varies with the energy density ($rho$) inside the compact object in presence of anisotropy with a pseudo-spheroidal geometry described by Vaidya-Tikekar metric. The density dependence of $B$ for different anisotropy including isotropic case is determined here. It is noted that although $B$ varies with anisotropy inside the star, finally at the surface it attains a value which is independent of the anisotropy. The Bag parameter $B$ is found to increase with an increase in anisotropy for a given compactness factor $(M/b)$ and spheroidicity parameter ($lambda$). It is also noted that for a star with given mass (M) and radius (b), the parameter $B$ increases with the increase of $lambda$ and finally at large value of $lambda$ it attains a constant value. We note that in this model equation of state (EoS) obtained from geometrical consideration with allowable value of ‘B’ is similar to that obtained by earlier investigators from consideration of microphysics. The stability of the stellar models for compact stars with anisotropy in hydro-static equilibrium is also studied.

General relativistic surface degrees of freedom in perturbed hybrid stars


Jonas Pereira (Nicolaus Copernicus Astronomical Center)

We study how the nature of a hybrid system (perfect fluid, solid or a mixture of them) could be related to the induction of general relativistic surface degrees of freedom on phase-splitting surfaces upon perturbation of its phases. We work in the scope of phase conversions in the vicinity of sharp phase transition surfaces whose timescales are either much smaller (rapid conversions) or larger (slow conversions) than the ones of the perturbations ($omega^{-1}$, where $omega$ is a characteristic frequency of oscillation of the star). In this first approach, perturbations are assumed to be purely radial. We show that surface degrees of freedom could emerge when either the core or the crust of a hybrid star is solid and phase conversions close to a phase-splitting surface are rapid. We also show how this would change the usual stability rule for solid hybrid stars, namely $partial M_0/partial rho_cgeq 0$, where $M_0$ is the total mass to the background hybrid star and $rho_c$ its central density. Further consequences of our analysis for asteroseismology are also discussed.

R3 - Tuesday 14:00-15:40 (Vanessa Graber)

Building mountains on accreting neutron stars


Ian Jones (Mathematical Sciences, University of Southampton)

The spin frequencies of the neutron stars in low-mass X-ray binaries may be limited by the emission of gravitational waves, potentially making them an interesting target for continuous gravitational wave searches. The gravitational waves may be produced by an asymmetry in the star’s mass distribution. Such “mountains” could be created by temperature asymmetries within the stellar crust. Little is currently known about the likely level of temperature asymmetry. We present our investigation of how internal magnetic fields might create such asymmetries, by making the thermal conductivity anisotropic.

Perturbation to a magnetic neutron star with shear modulus


Prasanta Bera (Mathemetical Science, University of Southampton)

The extent of the magnetic field at the interior of a neutron star is mostly unknown from the observed radiation features as it can probe up to the outer stellar surface. Theoretical models on the interior magnetic field geometry are generally oversimplified to avoid the complexity and mostly based on the axisymmetric barotropic fluid system. But these static magnetic equilibrium configurations are unstable with a short time scale against an infinitesimal perturbation to consider as a realistic model. The stellar material does not behave as a perfect fluid and the matter in the neutron star crust forms an ionic crystal. The electrostatic interactions between the crystallized charged particles can generate shear stress against any applied strain as a form of a perturbation. To incorporate the effect of crystallized crust on the dynamical evolution of the perturbed equilibrium structure, we study the effect of shear on the instability within the axisymmetric magnetic star. We find the limit of the critical shear modulus to prevent magnetic instability and the corresponding astrophysical consequences.

Deformations of neutron stars with elastic crusts


Fabian Gittins (University of Southampton)

With the recent, first detection of a binary neutron-star merger by gravitational-wave detectors it proves timely to consider how the internal structure of neutron stars affects the way in which they are deformed. Such deformations will leave measurable imprints on gravitational-wave signals and can be sourced through tidal interactions or the formation of mountains. In this talk, I will summarise the formalism that describes fully-relativistic neutron-star models with elastic crusts undergoing static perturbations. This formalism primes the problem for studies into a variety of different mechanisms that can deform a neutron star. I will present results from integrating the perturbation equations for tidally-deformed neutron stars with barotropic equations of state. These calculations enable us to compute interesting quantities such as the tidal Love number. I will show how to use the results from these integrations to show when and where the crust starts to fail during an inspiral.

The microscopic bulk and shear moduli of quantum nuclear pasta


William Newton (Physics and Astronomy, Texas A&M University-Commerce)

Using the results of the most extensive set of 3D, microscopic quantum calculations of nuclear pasta to date, under conditions relevant to the crusts of neutron stars, we perform the first quantum calculations of the bulk and shear moduli of the spaghetti phases in nuclear pasta. We perform a series of calculations of increasingly strained spaghetti configurations to find the stress-strain curves and the Poisson’s ratio of these phases of pasta. We thus obtain the microscopic Bulk Modulus of pasta and, using the obtained Poisson’s ratio, are able to transform that into a shear modulus. We will compare our results to those of classical nuclear pasta calculations, discuss how the results might scale to the macroscopic level and discuss implications for the generation of secular gravitational wave signals from mountains on neutron star crusts.

R4 - Tuesday 16:10-17:50 (Vanessa Graber)

Probing the interior of transiently accreting neutron stars


Nathalie Degenaar (Anton Pannekoek Institute for Astronomy, University of Amsterdam)

When residing in an X-ray binary, a neutron star accretes gas from a companion star. As matter accumulates on the neutron star surface, the underlying crust is compressed and heated due to nuclear reactions induced by this compression. These heating processes play an important role in setting the observable properties of thermonuclear bursts and rapid variability (mHz QPOs) observed from accreting neutron stars, and in the long-term thermal evolution of the neutron star core.

Once accretion switches off, sensitive X-ray satellites can be employed to observe the thermal glow of the accretion-heated crust and how it cools in absence of accretion. Comparing these observations with theoretical simulations provides very valuable insight into the structure and composition of neutron star crusts and core. I will present recent observational results from this method, which include new constraints on the superfluid properties of the dense neutron star core.

10 Years of accreting pulsars with Fermi-GBM


Christian Malacaria (NASA-MSFC/USRA)

We review 10 years of continuous monitoring of accretion-powered X-ray pulsars with the Gamma-ray Burst Monitor (GBM), the softer-energy all-sky monitoring instrument aboard the Fermi Gamma-ray Space Telescope.
The excellent combination of timing, spectral and full-sky coverage capabilities of GBM make it a unique instrument for the study of those objects.
After discussing our analysis approach we present the most interesting results for individual sources.
Over 10 years of operation, GBM helped to characterize spin histories, outbursts and torque behaviors of transient and persistent sources, deriving ephemeredis and orbital solutions for a variety of sources with high precision.
This, in turn, makes possible the study of binary systems, as well as the long term pulsars spin histories, two elements that are crucial to understanding the accretion processes onto magnetized neutron stars.
Recently, GBM played a fundamental role in discovering and characterizing the first Galactic Ultraluminous X-ray Pulsar, Swift J0243.6+6124.
After an outburst that took ~150 days, GBM kept monitoring the source thus revealing more intriguing aspects of its behavior.
This is emblematic of GBM capabilities and its exclusive scientific return.

Relativistic ocean $r$-modes during Type-I X-ray bursts


Frank Chambers (Anton Pannekoek Institute for Astronomy, University of Amsterdam)

Accreting neutron stars (NS) can exhibit high frequency modulations in their lightcurves during thermonuclear X-ray bursts, known as burst oscillations. These frequencies can be offset from the NS spin frequency by several Hz (where known independently) and can drift by $1-3$ Hz. One plausible explanation is that a wave is present in the bursting ocean, the rotating frame frequency of which is the offset. The frequency of the wave should decrease (in the rotating frame) as the burst cools hence explaining the drift. A strong candidate is a buoyant $r$-mode. To date, models that calculated the frequency of this mode taking into account the radial structure neglected relativistic effects and predicted rotating frame frequencies of $sim 4$~Hz and frequency drift of $> 5$~Hz; too large to be consistent with observations. I present a calculation that includes frame-dragging and gravitational redshift that reduces the rotating frame frequency by up to $30 %$ and frequency drift by up to $20 %$. Updating previous models for the ocean cooling in the aftermath of the burst to a model more representative of detailed calculations of thermonuclear X-ray bursts reduces the frequency of the mode still further. This model, combined with relativistic effects, can reduce the rotating frequency and frequency drift closer to observed values.

Fast flaring accretion state in the 69 ms pulsar A0538-66 revealed by XMM-Newton


Lorenzo Ducci (University of Tuebingen)

We carried out XMM-Newton observations of the 69 ms pulsar in the Be/X-ray binary (Be/XRB) A0538-66.
During these observations, the source showed a fast flaring activity never observed in this source nor in other Be/XRBs. Flares had durations between about 2 and 50 seconds and peak luminosities up to 4e38 erg/s (0.2-10 keV), with a luminosity dynamic range of about 2000.
Since its discovery, A0538-66 shows also a periodic fast flaring activity in the optical band, whose extreme properties have no similarities with those of other
binary systems.
We present the recent observational results and discuss the possible physical mechaninsms responsbile for the X-ray and optical variability of A0538-66.

R5 - Wednesday 14:00-15:40 (Vanessa Graber)

Flux-pinning-induced mutual friction force in the outer core of neutron stars and the rise of pulsar glitches


Aurélien Sourie (Institut d’Astronomie et d’Astrophysique, Université Libre de Bruxelles)

Pulsar glitches are commonly interpreted as sudden transfers of angular momentum from a more rapidly rotating superfluid component to the rest of the neutron star, triggered by large-scale vortex unpinning events. However, large uncertainties remain concerning, e.g., the microscopic interactions between the neutron vortices and the proton flux tubes that are expected to be present in the outer core of neutron stars. In particular, the possible pinning of vortex lines onto flux tubes may affect significantly the dynamical evolution of both the rotation and magnetic field of the star. Within this context, the neutron star core may thus provide a sufficient reservoir of angular momentum to explain giant glitches as observed in the Vela pulsar. In this talk, I will present our recent results about the role of the core neutron superfluid on the dynamics of the glitch rise.

Core and crust contributions in overshooting glitches: the Vela pulsar 2016 glitch


Alessandro Montoli (Università degli Studi di Milano)

During a pulsar glitch – the rapid acceleration of a neutron star in the otherwise steady spin down – the angular velocity of the star may overshoot, i.e. reach values greater than that of the new post-glitch equilibrium. In this talk a minimal analytical model will be presented, able to assess the presence of an overshoot. It will be employed to fit the data of the 2016 glitch of the Vela pulsar, obtaining estimates of the moments of inertia of the internal superfluid components involved in the glitch and of the spin-up and relaxation timescales. The results imply a reservoir of angular momentum extending beyond the crust and an inner core of non-superfluid matter.

Vortex-mediated mutual friction in neutron star crusts


Marco Antonelli (Nicolaus Copernicus Astronomical Centre of the Polish Academy of Sciences)

The inner crust of neutron stars is expected to contain an extended region of superfluid neutrons. A detailed description of this multi-component system remains to some extent unknown, leading to uncertainties in the macroscopic description of phenomena like glitches (sudden spin-up events detected in a pulsar) and neutron star oscillations. To capture correctly the physics of these macroscopic phenomena, hydrodynamic models have to be created: the key step is to understand how the dynamics of superfluid vortices scales up to a macroscopic description of the star. The vortex filament model (a classical description of a superfluid vortex line) may be used as a bridge between microscopic and macroscopic modelling of the superfluid in a neutron star crust. I will present preliminary results of numerical simulations of a superfluid vortex interacting with nuclei in the inner crust, indicating the important role played by the dissipative force damping the vortex motion.

Universality of the relativistic correction to glitch rise-times


Lorenzo Gavassino (Nicolaus Copernicus Astronomical Center (Warsaw))

Despite its importance in determining the interior structure of neutron stars has been universally acknowledged, Einstein’s theory of General Relativity has been up to now mostly neglected in the study of pulsar glitches. Its inclusion into the existing Newtonian models seems to be too expensive, compared to the moderate qualitative gain in accuracy and comprehension it gives. However, as the resolution of pulsar timing techniques increases, it will be soon important to be able to isolate the relativistic contributions to the glitch amplitude and rise-time, for a reliable quantitative comparison with observations. We will present, here, a simple universal formula for the relativistic correction to the glitch rise-time, given as a pure function of the compactness of the neutron star. It has been derived directly from Carter’s multifluid hydrodynamics and can be easily employed to correct, a posteriori, any Newtonian estimation for the coupling time scale, without any computational expense.

R6 - Wednesday 16:10-17:50 (Vanessa Graber)

Inferring properties of neutron stars using continuous gravitational-wave and long-term electromagnetic measurements


Patrick Meyers (Physics, University of Melbourne)

With the explosion of binary black hole systems that have been measured by LIGO and Virgo, it is clear that the era of gravitational-wave (GW) astrophysics is well underway. One of the next frontiers of GW astrophysics is the measurement of continuous GWs from rapidly rotating neutron stars. In this talk, we explore the implications of a measurement of continuous GWs on our understanding of neutron stars. We present an idealised two-component model for a neutron star that includes coupling between the crust and superfluid core, and stochastic terms to mimic timing noise and accretion. We then show that with sufficient GW and electromagnetic observations of the star it is possible to use state space identification techniques to infer parameters related to the coupling between the crust and core, as well as the covariances of the stochastic noise processes. We then propose extensions of this work to current situations like those of radio pulsars, where only electromagnetic measurements are currently available.

From multi-messenger observations to the neutron star equation of state


Margherita Fasano (Physics , La Sapienza – University of Rome)

Using a Bayesian approach, we combine measurements of neutron star macroscopic observables obtained by astrophysical and gravitational observations, to derive joint constraints on the equation of state (EoS) of matter at supranuclear density. In our analysis we use two sets of data: (i) the masses and tidal deformabilities measured in the binary neutron star event GW170817, detected by LIGO and Virgo; (ii) the masses and stellar radii measured from observations of nuclear bursts in accreting low-mass X-ray binaries. Using two different parametrizations of the equation of state, we compute the posteriorprobability distributions of the EoS parameters, using which we infer the posterior distribution for the radius and the mass of the two neutron stars of GW170817. The constraints we set on the radii are tighter than previous bounds.

Stability analysis of a differentially rotating, hot, hypermassive Neutron Star merger remnant


Sarmistha Banik (Physics, BITS Pilani, Hyderabad)

The stability of the merger remnant depends crucially on the underlying Equation of State (EoS) as well as the differential rotation velocity profile of the Neutron Stars(NS). Thus it provides a method to probe the nature of dense matter in NS cores, which is still a mystery, as the nature of dense matter beyond saturation density is not accessible to terrestrial experiments. The recent detection of NS merger event GW170817 has opened up a new window to the universe. Post-merger searches by the LIGO-VIRGO collaboration did not find evidence for GW from the remnant. One probable outcome is a differentially-rotating hot hypermassive neutron star. We consider the most realistic solutions of differentially rotating class “A” stars, which always have a mass-shedding limit. For this we consider zero-temperature as well as finite entropy EoSs based on the phenomenological Relativistic Mean Field (RMF) with density-dependent coefficients. We constructed relativistic equilibrium sequences of differentially rotating NSs and calculate the extra mass supported by the rotating star compared to the static star. We also generate equilibrium sequences with different degrees of differential rotation. For constant angular momentum sequences the onset of the secular instability is then marked by the ”Turning point” criterion i.e. the maximum of the gravitational masses as a function of central density. We also investigate whether the presence of strangeness affects the universality relations and find the existence of two families of curves of hot and cold stars for a differentially rotating star. We examine the universality with a range of differential rotation parameters as well. Finally we compute the collapse time of the NS merger remnant for the different EoSs and compared them with the window allowed by observations of progenitor mass from short gamma ray bursts and GW170817.

Timing of spider pulsars: what can we learn ?


Guillaume Voisin (Jodrell Bank Centre for Astrophysics, The University of Manchester)

Spider pulsars are composed of a millisecond pulsar (MSP) and a low-mass companion, forming the so-called black widows (companion mass Mc 0.1Msol). As MSPs these pulsars are privileged targets for precision timing and possibly gravitational-wave timing arrays, and there is evidence that these systems host the most massive neutron stars known to date (up to 2.4 Msun for PSR B1957+20!). However the complex interaction with their companion is still poorly understood and renders their behaviour virtually unpredictable by current models. Indeed, multiple spider pulsars are known to display significant orbital variability on month/year timescale which has long been suspected to be connected to the internal dynamics of the companion via changes in its quadrupole moment caused by, e.g., the Applegate mechanism.
In this talk I will review the state of the art of neutron-star mass determination and pulsar timing in spider systems. I will present a new timing model that extends the Damour and Deruelle model for relativistic binaries to systems with tidally and centrifugally deformed companions as well as internally generated quadrupole variations. We will then discuss applications of this model to existing data, and how it improves our understanding of these binaries.

R7 - Thursday 14:00-15:40 (Vanessa Graber)

Persistent Hard X-rays from Magnetar Magnetospheres


Matthew Baring (Physics and Astronomy, Rice University)

Magnetars are the most powerful compact objects in the stellar mass
range observed in the Milky Way. Periodicity seen in magnetar quiescent
and outburst emission, and distinctive “spin-down” lengthening of the
period have driven the paradigm that strongly-magnetized neutron stars
constitute these fascinating sources. Steady, pulsed hard X-ray emission
has been detected in about 10 magnetars, a magnetospheric signal that is
best modeled via inverse Compton scattering in their strong magnetic
fields. The scattering is resonant at the cyclotron frequency, thereby
enhancing its efficiency by a few orders of magnitude relative to the
familiar Thomson process. This paper discusses our recent exploration of
the generation of spectra, pulsation and polarization from toroidal
emission volumes in magnetar magnetospheres. Requiring the model spectra
to match the hard X-ray signals and not over-produce soft gamma-rays
constrains the electron Lorentz factor to below around 20. Comparison of
observed and model pulse profiles in the 10-150 keV band provides
constraints on the inclination of the magnetic dipole axis to the
rotation axis, and also on the observer viewing perspective. The paper
also discusses predictions of strong polarization and possible
attenuation signatures of exotic QED mechanisms like photon splitting
and magnetic pair creation, and the quest for their observational
vindication with future missions such as e-ASTROGAM and AMEGO.

Authors: Matthew G. Baring (presenter), Zorawar Wadiasingh, Alice K. Harding, Peter L. Gonthier & Kun Hu

Twisted magnetosphere in the exterior of a magnetar: GR at work in force-free magnetosphere


Yasufumi Kojima (Physics, Hiroshima University)

We calculate relativistic force-free magnetospheres twisted due to shearing motion at the surface, in order to examine a process of magnetic energy storage there. In a strongly twisted case, a magnetic flux rope, in which large amount of toroidal field is confined, is detached in vicinity of the star. General relativistic effect is very important to confine the flux rope. The magnetic energy in magnetosphere with the toroidal rope substantially increases, and the maximum exceeds open field energy. This means that a transition from close to open field-configurations is possible. The confined plasma and excess energy may be ejected as a magnetar giant flare/outburst.

Refs. Y. Kojima et al MNRAS 468(2017)2011;475(2018)5290;477(2018)3530 and ongoing work

General-relativistic pulsar magnetospheric emission


Quentin Giraud (Observatoire astronomique de Strasbourg)

Due to the high compactness of neutron stars, signatures of relativistic effects are expected in their vicinity, effects that will affect, among other things, the trajectory of photons produced inside their magnetosphere. In this talk, light curves and sky maps are plotted for radio and high energy photons, taken into account light bending and Shapiro delay within the Scharwzschild’s metric, comparing it to flat space-time. We simulated emission maps from curvature radiation in the magnetosphere of a pulsar following the polar cap and slot gap models. The objective of these researches is to determine a marker of general-relativistic effects in pulsars light curves, quantifying the significance of photon trajectory bending and Shapiro time-delay.

Semi analytical modelling of radio pulsar’s power spectra by implementing non-linear plasma process.


Tridib Roy (Astronomy and Astrophysics, Indian Institute Of Astrophysics jointly with pondicherry university)

There are basically three prominent processes in which electromagnetic waves can undergo scattering in an ambient plasma medium. First, one is very well known Compton scattering, it is the process when the scattering of radiation occurs by a single electron. Second and third ones are stimulated Raman scattering (SRS) and stimulated Compton scattering (SCS), which are the relatively less known plasma process phenomenon. By definition, SRS is a process, where the scattering of radiation occurs by longitudinal electron plasma mode whereas SCS occurs by highly damped electron plasma mode. In this article, we have explored the possibility of explaining the radio power spectra of pulsar under different circumstances of plasma. We have computed growth rate due to stimulated Raman scattering instability by using analytical formula (Drake et al. 1974; Liu and Kaw 1976) and growth rate due to stimulated Compton scattering instability numerically. Thereafter we have reproduced the full radio power spectrum of the following pulsar, PSR 2111+43 theoretically by assuming dispersion relation of un-magnetized plasma and the spatial variation associated with different plasma parameters like plasma density, Lorentz factor of electrons, frequency and input flux of the pump wave. So it is possible to generate an empirical formula for each and individual radio pulsars with different plasma index. Pump wave from background radiation in the pulsar magnetosphere interacts with relativistically moving electron jets, coming out from the pulsar surface. There exist some prevailing conditions on plasma parameters, when input radiation gets enhanced and backscattered, by interacting with electron jets. Let’s assume that electron jets do follow the Maxwellian distribution. Now If the phase velocity of background radiation or pump wave falls in the negative slope region of the velocity distribution curve of electrons, electrons will get back energy from the pump wave and in the positive slope region electrons will imparts energy to pump waves. As result electrons will suffer Landau damping and the scattered wave amplitude will grow with time and attain some non-linear unstable stage in positive slope region and finally dissipate energy in terms of radio emission. We have tried to model two-segmented broken power law and single power spectra of radio pulsars, by incorporating different constraints associated with the plasma parameters with a valid theoretical basis.

R8 - Friday 16:10-17:50 (Vanessa Graber)

Wave heating from proto-neutron star convection and the core-collapse supernova explosion mechanism


Sarah Gossan (Canadian Institute for Theoretical Astrophysics (CITA))

Our understanding of the core-collapse supernova explosion mechanism is incomplete. While the favored scenario is delayed revival of the stalled shock by neutrino heating, it is difficult to reliably compute explosion outcomes and energies, which depend sensitively on the complex radiation hydrodynamics of the post-shock region. For computational efficiency, many simulations mask out the inner regions of the proto-neutron star (PNS), from which nearly all the PNS binding energy and hence explosion energy originates. We show that gravity waves excited by core PNS convection can couple with outgoing acoustic waves that present an appreciable source of energy and pressure in the post-shock region. Using one-dimensional simulations, we estimate the gravity wave energy flux excited by PNS convection and the fraction of this energy transmitted upward to the post-shock region as acoustic waves. We find wave energy fluxes near 1051 erg s-1 likely persist for ~1 s post-bounce, well after neutrino heating rates have greatly decreased. The wave pressure on the shock may exceed 10% of the thermal pressure, potentially contributing to shock revival and, subsequently, a successful and energetic explosion. We discuss how future simulations can better capture the effects of waves and more accurately quantify wave heating rates.

The role of neutron star physics in binary driven hypernovae and gamma-ray bursts


Jorge Armando Rueda Hernandez (ICRANet, INAF, University of Ferrara)

A binary driven hypernova (BdHN) is produced in a compact binary composed of a carbon-oxygen (CO) star with a neutron star (NS) companion. The CO star explodes as supernova (SN) forming at its center a newborn NS and ejecting matter. The ejecta accretes onto the NS companion. For orbital periods of the order of 5 minutes, the accretion proceeds at high rates of up to 0.1 solar masses per second, thanks to the key role of neutrino emission. The NS reaches the critical mass and forms a black hole (BH). A new binary system composed of a newborn NS and a newborn BH is therefore formed. I present in this talk the relevance of all the physical processes associated with the above cataclismic event for the explanation of energetic long gamma-ray bursts (GRBs) associated with SNe. The role of the knowledge of the NS structure for the explanation of these high energetic processes emitting up to 10^54 erg in few seconds is discussed with the aid of three-dimensional SPH simulations, starting from X-ray precursor, to the prompt gamma-ray emission, to the high-energy and to the X-ray afterglow.