Jekyll2019-07-25T10:05:02+00:00http://core.gitpages.tpi.uni-jena.de/feed.xmlComputational RelativityCoRe collaboration website.Spiral-wave wind for the blue kilonova2019-07-10T00:00:00+00:002019-07-10T00:00:00+00:00http://core.gitpages.tpi.uni-jena.de/papers/2019/07/10/paper-spiralwavewind<p>In <a href="https://arxiv.org/abs/1907.04872">1907.04872</a> we investigate the new mechanism of mass ejection from the BNS systems after merger. We find that the interaction between the remnant, should it survive, and the disk creates a characteristic spiral wave structure in the latter and drives the quasi-steady state outflow with total mass ~10^{-2} solar masses and fine-tuned velocity around 0.2c and high electron fraction of >0.25. This spiral-wave wind persists as long as remnant lives and dies out quickly after the BH formation. Its properties are robust with resolution and inclusion of the subgird turbulence.
Then we use the data from numerical relativity simulations to compute the kilonova models. We report that the combination of dynamical ejecta and spiral-wave wind can account for early-time observed light curves.</p>V.NedoraIn 1907.04872 we investigate the new mechanism of mass ejection from the BNS systems after merger. We find that the interaction between the remnant, should it survive, and the disk creates a characteristic spiral wave structure in the latter and drives the quasi-steady state outflow with total mass ~10^{-2} solar masses and fine-tuned velocity around 0.2c and high electron fraction of >0.25. This spiral-wave wind persists as long as remnant lives and dies out quickly after the BH formation. Its properties are robust with resolution and inclusion of the subgird turbulence. Then we use the data from numerical relativity simulations to compute the kilonova models. We report that the combination of dynamical ejecta and spiral-wave wind can account for early-time observed light curves.Dynamical ejecta data2019-05-30T00:00:00+00:002019-05-30T00:00:00+00:00http://core.gitpages.tpi.uni-jena.de/core-database/2019/05/30/data-ejecta<p>We release dynamical ejecta data from binary neutron star merger simulations of</p>
<blockquote>
<p>D. Radice, A. Perego, K. Hotokezaka, S. A. Fromm, S. Bernuzzi, and L. F. Roberts, Binary Neutron Star Mergers: Mass Ejection, Electromagnetic Counterparts, and Nucleosynthesis, ApJ 869:130 (2018), arXiv:1809.11161</p>
</blockquote>
<p>The outflows are extracted at a fixed coordinate sphere with radius 300 G/c^2 Msun (= 443 km). Only material unbound according to the geodesic criterion is considered to be part of the dynamical ejecta.</p>
<p>Data are relased on <a href="https://zenodo.org/record/3235675#.XPAjxENS-00">ZENODO</a></p>
<p>Included data:</p>
<ul>
<li><code class="highlighter-rouge">Table2.txt</code>: Table 2 of the paper in machine readable format</li>
<li><code class="highlighter-rouge">tabulated_nucsyn.h5</code>: nucleosynthesis yields from pre-computed parametrized trajectories. The first three indices of each dataset are Ye, entropy, and expansion timescale tau. For example <code class="highlighter-rouge">Y_final[iYe, ientr, itau, iiso]</code> gives the final abundance of isotope <code class="highlighter-rouge">iiso</code> with <code class="highlighter-rouge">A[iiso]</code> and <code class="highlighter-rouge">Z[iiso]</code> for a trajectory with initial Ye = <code class="highlighter-rouge">Ye[iYe]</code>, initial entropy <code class="highlighter-rouge">s[ientr]</code>, and expansion timescale <code class="highlighter-rouge">tau[itau]</code>.</li>
<li><code class="highlighter-rouge">[model].tar</code>: ejecta data for individual simulations. The naming convention is the same as in the paper.</li>
</ul>
<p>For each model we provide:</p>
<ul>
<li><code class="highlighter-rouge">outflow.txt</code>: angle integrated outflow rate and cumulated ejecta mass. Data are given in units with Msun = G = c = 1 (eg, the conversion factor for time to seconds is 4.9258e-6).</li>
<li><code class="highlighter-rouge">hist_entropy.dat</code>: histogram of the ejecta as a function of the entropy (in kb)</li>
<li><code class="highlighter-rouge">hist_vinf.dat</code>: histogram of the ejecta as a function of the asymptotic velocity (in units of c)</li>
<li><code class="highlighter-rouge">hist_ye.dat</code>: histogram of the ejecta as a function of the electron fraction Ye.</li>
<li><code class="highlighter-rouge">profile.txt</code>: time integrated ejecta profiles as a function of the polar angle.</li>
<li><code class="highlighter-rouge">hist_vinf_theta.h5</code>: histograms of the ejecta as a function of the asymptotic velocity and the polar angle.</li>
<li><code class="highlighter-rouge">hist_ye_theta.h5</code>: histograms of the ejecta as a function of the asymptotic velocity and the polar angle.</li>
<li><code class="highlighter-rouge">hist_ye_entropy_tau.h5</code>: histograms of the ejecta as a function of Ye, entropy, and expansion timescale tau.</li>
</ul>
<p>Additionally we distribute:</p>
<ul>
<li>Initial data generated with LORENE and associated EOS tables.</li>
<li>EOS tables used for the evolution</li>
<li>Parameter file used for each simulation</li>
</ul>
<p>For the multidimensional histograms the indices are ordered as specified in the file name, ie the file <code class="highlighter-rouge">hist_ye_theta.h5</code> tabulates the ejecta mass as a function of Ye (first index) and polar angle theta (second index).</p>CoRe-adminWe release dynamical ejecta data from binary neutron star merger simulations ofImproving the NRTidal model for binary neutron star systems2019-05-15T00:00:00+00:002019-05-15T00:00:00+00:00http://core.gitpages.tpi.uni-jena.de/papers/2019/05/15/paper-nrtidalv2<p>In <a href="https://arxiv.org/abs/1905.06011">1905.06011</a> we present
an extension of the NRTidal model for binary neutron star (BNS) waveforms.
The upgrades are: (i) a new closed-form expression for the tidal contribution to the GW phase which
includes further analytical knowledge and is calibrated to more accurate numerical relativity data
than previously available; (ii) a tidal correction to the GW amplitude; (iii) an extension of the spinsector incorporating equation-of-state-dependent finite size effects at quadrupolar and octupolar
order; these appear in the spin-spin tail terms and cubic-in-spin terms, both at 3.5PN.
We add the new description to the precessing binary black hole waveform model IMRPhenomPv2
to obtain a frequency-domain precessing binary neutron star model. In addition, we extend the
SEOBNRv4_ROM and IMRPhenomD aligned-spin binary black hole waveform models with the improved
tidal phase corrections. Focusing on the new IMRPhenomPv2_NRTidalv2 approximant, we test the
model by comparing with numerical relativity waveforms as well as hybrid waveforms combining
tidal effective-one-body and numerical relativity data. We also check consistency against a tidal
effective-one-body model across large regions of the BNS parameter space</p>T.DietrichIn 1905.06011 we present an extension of the NRTidal model for binary neutron star (BNS) waveforms. The upgrades are: (i) a new closed-form expression for the tidal contribution to the GW phase which includes further analytical knowledge and is calibrated to more accurate numerical relativity data than previously available; (ii) a tidal correction to the GW amplitude; (iii) an extension of the spinsector incorporating equation-of-state-dependent finite size effects at quadrupolar and octupolar order; these appear in the spin-spin tail terms and cubic-in-spin terms, both at 3.5PN. We add the new description to the precessing binary black hole waveform model IMRPhenomPv2 to obtain a frequency-domain precessing binary neutron star model. In addition, we extend the SEOBNRv4_ROM and IMRPhenomD aligned-spin binary black hole waveform models with the improved tidal phase corrections. Focusing on the new IMRPhenomPv2_NRTidalv2 approximant, we test the model by comparing with numerical relativity waveforms as well as hybrid waveforms combining tidal effective-one-body and numerical relativity data. We also check consistency against a tidal effective-one-body model across large regions of the BNS parameter spaceBlack-hole remnants from black-hole–neutron-star mergers2019-03-19T00:00:00+00:002019-03-19T00:00:00+00:00http://core.gitpages.tpi.uni-jena.de/papers/2019/03/19/paper-bhnsremnant<p>In <a href="https://arxiv.org/abs/1903.11622">1903.11622</a> we construct a model for the remnant black hole produced by the collision of stellar-mass black holes and a neutron stars mergers (BHNS). We used a sample of numerical-relativity simulations and mapped the properties of the binary components to the mass and spin of the remnant black hole in a simple and physically accurate way.</p>
<p>As an application, we combine the remnant characterization with state-of-art population synthesis for binary formation. We predict that BHNS mergers produce a population of remnant black holes with masses narrowly distributed around 7M⊙ and 9M⊙. Assuming isotropic spin distribution of the initial BH implies that nonmassive accretion disks are favoured: no bright electromagnetic counterparts are expected in such mergers.</p>
<p>Our results will support LIGO-Virgo observations of BHNS systems as new sources of gravitational waves and the joint analysis with electromagnetic signals. While they predict (and will eventually explain) the lack of electromagnetic counterparts for these events, they also point out that a counterpart observation will heavily impact the most unknown physics: astrophysical spin distributions of the BH in the binary and the NS equation of state.</p>
<p>A python code of our model can be found <a href="https://git.tpi.uni-jena.de/core/bhnsremnant">here</a></p>S.BernuzziIn 1903.11622 we construct a model for the remnant black hole produced by the collision of stellar-mass black holes and a neutron stars mergers (BHNS). We used a sample of numerical-relativity simulations and mapped the properties of the binary components to the mass and spin of the remnant black hole in a simple and physically accurate way.Thermodynamics conditions of matter in neutron star mergers2019-03-19T00:00:00+00:002019-03-19T00:00:00+00:00http://core.gitpages.tpi.uni-jena.de/papers/2019/03/19/paper-thermodynamicsbns<p>In <a href="https://arxiv.org/abs/1903.07898">1903.07898</a> we explore the
properties of extreme matter along the general relativistic dynamics
of neutron star mergers. We consider 3 microphysical equations of
state and numerical relativity simulations including an approximate
neutrino transport scheme and construct time-dependent histograms of
the mass on a 3D hypersurfaces as distributed in density, temperature
and electron fraction bins (see figure below). For example, the matter
in a merger ending in a long-lived neutron star increases the initial
maximum density up to ∼3-4ρ0 (ρ0 is the nuclear saturation density),
and the multiple centrifugal bounces heat the initially cold matter to
several tens of MeV. Streams of hot matter with initial densities ∼2ρ0
move outwards and cool due to decompression and neutrino emission. The
remnant reaches temperatures up to 50 MeV, but the highest
temperatures are confined in an approximately spherical annulus at
∼ρ0. Such temperatures favour positron-neutron capture and lead to a
neutrino emission dominated by electron antineutrinos. Neutrinos are
trapped at the highest densities of the remnant core which is less
affected by weak interaction and only at longer timescales. A similar
dynamics is found if the remnant collapses to black hole. The main
difference bewteen the two case is found in the remnant disk. Both
discs are neutron rich and not isentropic, but they differ in size,
entropy and lepton fraction depending on the nature of the central
object. In presence of a black hole, disks are smaller and mostly
transparent to neutrinos; in presence of a massive neutron star, they
are more massive, geometrically and optically thick.</p>S.BernuzziIn 1903.07898 we explore the properties of extreme matter along the general relativistic dynamics of neutron star mergers. We consider 3 microphysical equations of state and numerical relativity simulations including an approximate neutrino transport scheme and construct time-dependent histograms of the mass on a 3D hypersurfaces as distributed in density, temperature and electron fraction bins (see figure below). For example, the matter in a merger ending in a long-lived neutron star increases the initial maximum density up to ∼3-4ρ0 (ρ0 is the nuclear saturation density), and the multiple centrifugal bounces heat the initially cold matter to several tens of MeV. Streams of hot matter with initial densities ∼2ρ0 move outwards and cool due to decompression and neutrino emission. The remnant reaches temperatures up to 50 MeV, but the highest temperatures are confined in an approximately spherical annulus at ∼ρ0. Such temperatures favour positron-neutron capture and lead to a neutrino emission dominated by electron antineutrinos. Neutrinos are trapped at the highest densities of the remnant core which is less affected by weak interaction and only at longer timescales. A similar dynamics is found if the remnant collapses to black hole. The main difference bewteen the two case is found in the remnant disk. Both discs are neutron rich and not isentropic, but they differ in size, entropy and lepton fraction depending on the nature of the central object. In presence of a black hole, disks are smaller and mostly transparent to neutrinos; in presence of a massive neutron star, they are more massive, geometrically and optically thick.Large-scale Gauss allocation on SuperMUC at LRZ2018-10-29T00:00:00+00:002018-10-29T00:00:00+00:00http://core.gitpages.tpi.uni-jena.de/computing/2018/10/29/computing-gauss<p>The Jena group and the CoRe collaboration have been granted a large-scale Gauss allocation of 75M CPU-hrs on the SuperMUC supercomputer at LRZ.</p>CoRe-adminThe Jena group and the CoRe collaboration have been granted a large-scale Gauss allocation of 75M CPU-hrs on the SuperMUC supercomputer at LRZ.Viscous-dynamical ejecta in asymmetric binary neutron star mergers2018-10-05T00:00:00+00:002018-10-05T00:00:00+00:00http://core.gitpages.tpi.uni-jena.de/papers/2018/10/05/paper-viscousdynejecta<p>In <a href="https://arxiv.org/abs/1809.11163">1809.11163</a> we report about new
mass outflow mechanism operating in unequal mass binaries on dynamical
timescales and enabled by turbulent viscosity. <em>Viscous-dynamical
ejecta</em> are launched during merger due to the thermalization of
mass exchange streams between the secondary and the primary neutron
star. They are characterized by asymptotic velocities extending up to
0.8 c, and have masses that depend on the efficiency of the viscous
mechanism. For values of the viscous parameter expected to arise from
magnetohydrodynamics instabilities operating during merger, viscosity
is found to enhance the overall mass of the dynamical ejecta by a
factor of a few and the mass of the fast tail of the ejecta having
asymptotic velocities > 0.6 c by up to four orders of magnitude.</p>CoRe-adminIn 1809.11163 we report about new mass outflow mechanism operating in unequal mass binaries on dynamical timescales and enabled by turbulent viscosity. Viscous-dynamical ejecta are launched during merger due to the thermalization of mass exchange streams between the secondary and the primary neutron star. They are characterized by asymptotic velocities extending up to 0.8 c, and have masses that depend on the efficiency of the viscous mechanism. For values of the viscous parameter expected to arise from magnetohydrodynamics instabilities operating during merger, viscosity is found to enhance the overall mass of the dynamical ejecta by a factor of a few and the mass of the fast tail of the ejecta having asymptotic velocities > 0.6 c by up to four orders of magnitude.Dynamical ejecta from neutron star mergers2018-10-04T00:00:00+00:002018-10-04T00:00:00+00:00http://core.gitpages.tpi.uni-jena.de/papers/2018/10/04/paper-dynamicalejecta<p>In <a href="https://arxiv.org/abs/1809.11161">1809.11161</a> we present a systematic
numerical relativity study of the mass ejection and the
associated electromagnetic transients and nucleosynthesis from
binary neutron star mergers. The paper was lead by David
Radice and with key contributions from Albino Perego
(kilonova), Kenta Hotokezaka (radio light cuvres), Steven
Fromm and Luke Roberts (nucleosynthesis). It reports a
comprehensive analysis of the largest sample of simulations
performed to date. All the simulations include neutrino
transport and microphysics and are performed at high grid
resolutions and with state-of-art numerical methods. We find
that a few 1e-3 M⊙ of material are ejected dynamically during
the mergers. The amount and the properties of these outflow
depend on binary parameters and on the NS equation of state
(EOS). A small fraction of these ejecta, typically ∼ 1e-6 M⊙,
is accelerated by shocks formed shortly after merger to
velocities larger than 0.6c and produces bright radio flares
on timescales of weeks, months, or years after merger. Their
observation could constrain the strength with which the NSs
bounce after merger and, consequently, the EOS of matter at
extreme densities. The dynamical ejecta robustly produce
second and third r-process peak nuclei with relative isotopic
abundances close to solar. The production of light r-process
elements is instead sensitive to the binary mass ratio and the
neutrino radiation treatment. Accretion disks of up to ∼0.2M⊙
are formed after merger, depending on the lifetime of the
remnant. In most cases, neutrino- and viscously-driven winds
from these disks dominate the overall outflow. We generate
synthetic kilonova light curves and find that kilonovae depend
on the merger outcome and could be used to constrain the NS
EOS.</p>S.BernuzziIn 1809.11161 we present a systematic numerical relativity study of the mass ejection and the associated electromagnetic transients and nucleosynthesis from binary neutron star mergers. The paper was lead by David Radice and with key contributions from Albino Perego (kilonova), Kenta Hotokezaka (radio light cuvres), Steven Fromm and Luke Roberts (nucleosynthesis). It reports a comprehensive analysis of the largest sample of simulations performed to date. All the simulations include neutrino transport and microphysics and are performed at high grid resolutions and with state-of-art numerical methods. We find that a few 1e-3 M⊙ of material are ejected dynamically during the mergers. The amount and the properties of these outflow depend on binary parameters and on the NS equation of state (EOS). A small fraction of these ejecta, typically ∼ 1e-6 M⊙, is accelerated by shocks formed shortly after merger to velocities larger than 0.6c and produces bright radio flares on timescales of weeks, months, or years after merger. Their observation could constrain the strength with which the NSs bounce after merger and, consequently, the EOS of matter at extreme densities. The dynamical ejecta robustly produce second and third r-process peak nuclei with relative isotopic abundances close to solar. The production of light r-process elements is instead sensitive to the binary mass ratio and the neutrino radiation treatment. Accretion disks of up to ∼0.2M⊙ are formed after merger, depending on the lifetime of the remnant. In most cases, neutrino- and viscously-driven winds from these disks dominate the overall outflow. We generate synthetic kilonova light curves and find that kilonovae depend on the merger outcome and could be used to constrain the NS EOS.Relevance of tidal effects and post-merger dynamics for binary neutron star parameter estimation2018-08-29T00:00:00+00:002018-08-29T00:00:00+00:00http://core.gitpages.tpi.uni-jena.de/papers/2018/08/29/paper-relevancetides<p>In <a href="https://arxiv.org/abs/1808.09749">1808.09749</a> we use complete inspiral–merger–post-merger waveforms constructed from a tidal effective-one-body approach and numerical-relativity simulations as signals against which we perform parameter estimates with waveform models of standard LIGO-Virgo analyses. We show that neglecting tidal effects does not lead to appreciable measurement biases in masses and spin for typical observations. However, with increasing signal-to-noise ratio or tidal deformability there are biases in the estimates of the binary parameters.</p>CoRe-adminIn 1808.09749 we use complete inspiral–merger–post-merger waveforms constructed from a tidal effective-one-body approach and numerical-relativity simulations as signals against which we perform parameter estimates with waveform models of standard LIGO-Virgo analyses. We show that neglecting tidal effects does not lead to appreciable measurement biases in masses and spin for typical observations. However, with increasing signal-to-noise ratio or tidal deformability there are biases in the estimates of the binary parameters.CoRe database is online2018-04-12T00:00:00+00:002018-04-12T00:00:00+00:00http://core.gitpages.tpi.uni-jena.de/core-database/2018/04/12/data-gwdb<p>The Computational Relativity collaboration’s public database of gravitational waveforms from binary neutron star mergers is online. The database currently contains 367 waveforms from numerical simulations. It spans 164 physically distinct configuration with different binary parameters (total binary mass, mass-ratio, initial separation, eccentricity, and stars spins) and simulated physics. Waveforms computed at multiple grid resolutions and extraction radii are provided for controlling numerical uncertainties. These data are labelled as BAM:0001-BAM:0127 and THC:0001-THC:0015. We also release an exemplary set of 18 hybrid waveforms constructed with TEOBResumS.</p>CoRe-adminThe Computational Relativity collaboration’s public database of gravitational waveforms from binary neutron star mergers is online. The database currently contains 367 waveforms from numerical simulations. It spans 164 physically distinct configuration with different binary parameters (total binary mass, mass-ratio, initial separation, eccentricity, and stars spins) and simulated physics. Waveforms computed at multiple grid resolutions and extraction radii are provided for controlling numerical uncertainties. These data are labelled as BAM:0001-BAM:0127 and THC:0001-THC:0015. We also release an exemplary set of 18 hybrid waveforms constructed with TEOBResumS.