96 research outputs found
A New Multi-Energy Neutrino Radiation-Hydrodynamics Code in Full General Relativity and Its Application to Gravitational Collapse of Massive Stars
We present a new multi-dimensional radiation-hydrodynamics code for massive
stellar core-collapse in full general relativity (GR). Employing an M1
analytical closure scheme, we solve spectral neutrino transport of the
radiation energy and momentum based on a truncated moment formalism. Regarding
neutrino opacities, we take into account a baseline set in state-of-the-art
simulations, in which inelastic neutrinoelectron scattering, thermal neutrino
production via pair annihilation and nucleonnucleon bremsstrahlung are
included. While the Einstein field equations and the spatial advection terms in
the radiation-hydrodynamics equations are evolved explicitly, the source terms
due to neutrino-matter interactions and energy shift in the radiation moment
equations are integrated implicitly by an iteration method. To verify our code,
we first perform a series of standard radiation tests with analytical solutions
that include the check of gravitational redshift and Doppler shift. A good
agreement in these tests supports the reliability of the GR multi-energy
neutrino transport scheme. We then conduct several test simulations of
core-collapse, bounce, and shock-stall of a 15Msun star in the Cartesian
coordinates and make a detailed comparison with published results. Our code
performs quite well to reproduce the results of full-Boltzmann neutrino
transport especially before bounce. In the postbounce phase, our code basically
performs well, however, there are several differences that are most likely to
come from the insufficient spatial resolution in our current 3D-GR models. For
clarifying the resolution dependence and extending the code comparison in the
late postbounce phase, we discuss that next-generation Exaflops-class
supercomputers are at least needed.Comment: 61 pages, 20 figures, accepted for publication in ApJ
Impact of magnetic field on neutrino-matter interactions in core-collapse supernova
We explore the impact of magnetic field on neutrino-matter interactions in
core-collapse supernova. We first derive the modified source terms for
neutrino-nucleon scattering and neutrino absorption and emission processes in
the moment formalism. Then we perform full relativistic three-dimensional,
magnetorotational core-collapse supernova simulations of a 20 star
with spectral neutrino transport. Our simulations treat self-consistently the
parity violation effects of weak interaction in the presence of external
magnetic field. The result shows a significant global asymmetry, mostly
confined in the proto-neutron star, with clearly reflecting the magnetic field
structure. The asymmetric property arises from two factors: the angle between
the neutrino flux and magnetic field, and the term, which is parallel to the
magnetic field and is also proportional to the deviation of distribution
function of neutrinos from thermal equilibrium. The typical correction value
amounts to % relative to the total neutrino-matter interaction rate for
the magnetic field strength of ~G. Although these asymmetric
properties do not immediately affect the explosion dynamics, our results imply
that they would be significant once the neutrinos diffuse out the proto-neutron
star core carrying those asymmetries away. We also show that, during our
simulation time of ms after bounce, our results indicate that the
correction value due to the modified inelastic scattering process dominates
over that of the modified neutrino absorption and emission process.Comment: 21 pages, 8 figures; accepted for publication in Ap
A New Gravitational-Wave Signature from Standing Accretion Shock Instabilities in Supernovae
We present results from fully relativistic three-dimensional core-collapse
supernova (CCSN) simulations of a non-rotating 15 Msun star using three
different nuclear equations of state (EoSs). From our simulations covering up
to ~350 ms after bounce, we show that the development of the standing accretion
shock instability (SASI) differs significantly depending on the stiffness of
nuclear EoS. Generally, the SASI activity occurs more vigorously in models with
softer EoS. By evaluating the gravitational-wave (GW) emission, we find a new
GW signature on top of the previously identified one, in which the typical GW
frequency increases with time due to an accumulating accretion to the
proto-neutron star (PNS). The newly observed quasi-periodic signal appears in
the frequency range from ~100 to 200 Hz and persists for ~150 ms before
neutrino-driven convection dominates over the SASI. By analyzing the cycle
frequency of the SASI sloshing and spiral modes as well as the mass accretion
rate to the emission region, we show that the SASI frequency is correlated with
the GW frequency. This is because the SASI-induced temporary perturbed mass
accretion strike the PNS surface, leading to the quasi-periodic GW emission.
Our results show that the GW signal, which could be a smoking-gun signature of
the SASI, is within the detection limits of LIGO, advanced Virgo, and KAGRA for
Galactic events.Comment: 7 pages, 5 figures, Accepted for publication in ApJ
Probing mass-radius relation of protoneutron stars from gravitational-wave asteroseismology
The gravitational-wave (GW) asteroseismology is a powerful technique for
extracting interior information of compact objects. In this work, we focus on
spacetime modes, the so-called -modes, of GWs emitted from a proto-neutron
star (PNS) in the postbounce phase of core-collapse supernovae. Using results
from recent three-dimensional supernova models, we study how to infer the
properties of the PNS based on a quasi-normal mode analysis in the context of
the GW asteroseismology. We find that the -mode frequency multiplied by
the PNS radius is expressed as a linear function with respect to the ratio of
the PNS mass to the PNS radius. This relation is insensitive to the nuclear
equation of state (EOS) employed in this work. Combining with another universal
relation of the -mode oscillations, we point out that the time dependent
mass-radius relation of the PNS can be obtained by observing both the - and
-mode GWs simultaneously. Our results suggest that the simultaneous
detection of the two modes could provide a new probe into finite-temperature
nuclear EOS that predominantly determines the PNS evolution.Comment: accepted for publication in PR
Systematic Features of Axisymmetric Neutrino-Driven Core-Collapse Supernova Models in Multiple Progenitors
We present an overview of two-dimensional (2D) core-collapse supernova
simulations employing neutrino transport scheme by the isotropic diffusion
source approximation. We study 101 solar-metallicity, 247 ultra metal-poor, and
30 zero-metal progenitors covering zero-age main sequence mass from to . Using the 378 progenitors in total, we
systematically investigate how the differences in the structures of these
multiple progenitors impact the hydrodynamics evolution. By following a
long-term evolution over 1.0 s after bounce, most of the computed models
exhibit neutrino-driven revival of the stalled bounce shock at 200 - 800
ms postbounce, leading to the possibility of explosion. Pushing the boundaries
of expectations in previous one-dimensional (1D) studies, our results confirm
that the compactness parameter that characterizes the structure of the
progenitors is also a key in 2D to diagnose the properties of neutrino-driven
explosions. Models with high undergo high ram pressure from the accreting
matter onto the stalled shock, which affects the subsequent evolution of the
shock expansion and the mass of the protoneutron star under the influence of
neutrino-driven convection and the standing accretion-shock instability. We
show that the accretion luminosity becomes higher for models with high ,
which makes the growth rate of the diagnostic explosion energy higher and the
synthesized nickel mass bigger. We find that these explosion characteristics
tend to show a monotonic increase as a function of the compactness parameter
.Comment: 15 pages, 22 figures, 277 progenitors added, accepted to PAS
Correlated Signatures of Gravitational-Wave and Neutrino Emission in Three-Dimensional General-Relativistic Core-Collapse Supernova Simulations
We present results from general-relativistic (GR) three-dimensional (3D)
core-collapse simulations with approximate neutrino transport for three
non-rotating progenitors (11.2, 15, and 40 Msun) using different nuclear
equations of state (EOSs). We find that the combination of progenitor's higher
compactness at bounce and the use of softer EOS leads to stronger activity of
the standing accretion shock instability (SASI). We confirm previous
predications that the SASI produces characteristic time modulations both in
neutrino and gravitational-wave (GW) signals. By performing a correlation
analysis of the SASI-modulated neutrino and GW signals, we find that the
correlation becomes highest when we take into account the time-delay effect due
to the advection of material from the neutrino sphere to the proto-neutron star
core surface. Our results suggest that the correlation of the neutrino and GW
signals, if detected, would provide a new signature of the vigorous SASI
activity in the supernova core, which can be hardly seen if neutrino-convection
dominates over the SASI.Comment: 24 pages, 10 figures, Accepted for publication in Ap
Coherent Network Analysis of Gravitational Waves from Three-Dimensional Core-Collapse Supernova Models
Using predictions from three-dimensional (3D) hydrodynamics simulations of
core-collapse supernovae (CCSNe), we present a coherent network analysis to
detection, reconstruction, and the source localization of the
gravitational-wave (GW) signals. We use the {\tt RIDGE} pipeline for the
analysis, in which the network of LIGO Hanford, LIGO Livingston, VIRGO, and
KAGRA is considered. By combining with a GW spectrogram analysis, we show that
several important hydrodynamics features in the original waveforms persist in
the waveforms of the reconstructed signals. The characteristic excess in the
spectrograms originates not only from rotating core-collapse, bounce and the
subsequent ring down of the proto-neutron star (PNS) as previously identified,
but also from the formation of magnetohydrodynamics jets and non-axisymmetric
instabilities in the vicinity of the PNS. Regarding the GW signals emitted near
at the rotating core bounce, the horizon distance extends up to 18 kpc
for the most rapidly rotating 3D model in this work. Following the rotating
core bounce, the dominant source of the GW emission shifts to the
non-axisymmetric instabilities. The horizon distances extend maximally up to
40 kpc seen from the spin axis. With an increasing number of 3D models
trending towards explosion recently, our results suggest that in addition to
the best studied GW signals due to rotating core-collapse and bounce, the time
is ripe to consider how we can do science from GWs of CCSNe much more seriously
than before. Particularly the quasi-periodic signals due to the
non-axisymmetric instabilities and the detectability should deserve further
investigation to elucidate the inner-working of the rapidly rotating CCSNe.Comment: PRD in pres
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