13 research outputs found
Generic Gravitational Wave Signals from the Collapse of Rotating Stellar Cores
We perform general relativistic simulations of stellar core collapse to a proto-neutron star, using a microphysical equation of state as well as an approximate description of deleptonization. We show that for a wide variety of rotation rates and profiles the gravitational wave burst signals from the core bounce are of a generic type, known as Type I in the literature. In our systematic study, using both general relativity and Newtonian gravity, we identify and individually quantify the micro- and macrophysical mechanisms leading to this result, i.e. the effects of rotation, the equation of state, and deleptonization. Such a generic type of signal templates will likely facilitate a more efficient search in current and future gravitational wave detectors of both interferometric and resonant type
The gravitational wave burst signal from core collapse of rotating stars
We present results from detailed general relativistic simulations of stellar
core collapse to a proto-neutron star, using two different microphysical
nonzero-temperature nuclear equations of state as well as an approximate
description of deleptonization during the collapse phase. Investigating a wide
variety of rotation rates and profiles as well as masses of the progenitor
stars and both equations of state, we confirm in this very general setup the
recent finding that a generic gravitational wave burst signal is associated
with core bounce, already known as type I in the literature. The previously
suggested type II (or "multiple-bounce") waveform morphology does not occur.
Despite this reduction to a single waveform type, we demonstrate that it is
still possible to constrain the progenitor and postbounce rotation based on a
combination of the maximum signal amplitude and the peak frequency of the
emitted gravitational wave burst. Our models include to sufficient accuracy the
currently known necessary physics for the collapse and bounce phase of
core-collapse supernovae, yielding accurate and reliable gravitational wave
signal templates for gravitational wave data analysis. In addition, we assess
the possiblity of nonaxisymmetric instabilities in rotating nascent
proto-neutron stars. We find strong evidence that in an iron core-collapse
event the postbounce core cannot reach sufficiently rapid rotation to become
subject to a classical bar-mode instability. However, many of our postbounce
core models exhibit sufficiently rapid and differential rotation to become
subject to the recently discovered dynamical instability at low rotation rates.Comment: 28 pages, 23 figures, minor change
Searching for prompt signatures of nearby core-collapse supernovae by a joint analysis of neutrino and gravitational-wave data
We discuss the science motivations and prospects for a joint analysis of
gravitational-wave (GW) and low-energy neutrino data to search for prompt
signals from nearby supernovae (SNe). Both gravitational-wave and low-energy
neutrinos are expected to be produced in the innermost region of a
core-collapse supernova, and a search for coincident signals would probe the
processes which power a supernova explosion. It is estimated that the current
generation of neutrino and gravitational-wave detectors would be sensitive to
Galactic core-collapse supernovae, and would also be able to detect
electromagnetically dark SNe. A joint GW-neutrino search would enable
improvements to searches by way of lower detection thresholds, larger distance
range, better live-time coverage by a network of GW and neutrino detectors, and
increased significance of candidate detections. A close collaboration between
the GW and neutrino communities for such a search will thus go far toward
realizing a much sought-after astrophysics goal of detecting the next nearby
supernova.Comment: 10 pages, 3 figures. To appear in Class. Quantum Gra
Determination of the angular momentum distribution of supernovae from gravitational wave observations
Significant progress has been made in the development of an international
network of gravitational wave detectors, such as TAMA300, LIGO, VIRGO, and
GEO600. For these detectors, one of the most promising sources of gravitational
waves are core collapse supernovae especially in our Galaxy. Recent simulations
of core collapse supernovae, rigorously carried out by various groups, show
that the features of the waveforms are determined by the rotational profiles of
the core, such as the rotation rate and the degree of the differential rotation
prior to core-collapse. Specifically, it has been predicted that the sign of
the second largest peak in the gravitational wave strain signal is negative if
the core rotates cylindrically with strong differential rotation. The sign of
the second peak could be a nice indicator that provides us with information
about the angular momentum distribution of the core, unseen without
gravitational wave signals. Here we present a data analysis procedure aiming at
the detection of the second peak using a coherent network analysis and estimate
the detection efficiency when a supernova is at the sky location of the
Galactic center. The simulations showed we were able to determine the sign of
the second peak under an idealized condition of a network of gravitational wave
detectors if a supernova occurs at the Galactic center.Comment: 9 pages, 11 figures, add references and some sentenses. To appear on
CQ
Axisymmetric general relativistic simulations of the accretion-induced collapse of white dwarfs
The accretion-induced collapse (AIC) of a white dwarf may lead to the formation of a protoneutron star
and a collapse-driven supernova explosion. This process represents a path alternative to thermonuclear
disruption of accreting white dwarfs in type Ia supernovae. In the AIC scenario, the supernova explosion
energy is expected to be small and the resulting transient short-lived, making it hard to detect by
electromagnetic means alone. Neutrino and gravitational-wave (GW) observations may provide crucial
information necessary to reveal a potential AIC. Motivated by the need for systematic predictions of the
GW signature of AIC, we present results from an extensive set of general-relativistic AIC simulations
using a microphysical finite-temperature equation of state and an approximate treatment of deleptonization
during collapse. Investigating a set of 114 progenitor models in axisymmetric rotational equilibrium,
with a wide range of rotational configurations, temperatures and central densities, and resulting white
dwarf masses, we extend previous Newtonian studies and find that the GW signal has a generic shape akin
to what is known as a ‘‘type III’’ signal in the literature. Despite this reduction to a single type of
waveform, we show that the emitted GWs carry information that can be used to constrain the progenitor
and the postbounce rotation. We discuss the detectability of the emitted GWs, showing that the signal-tonoise
ratio for current or next-generation interferometer detectors could be high enough to detect such
events in our Galaxy. Furthermore, we contrast the GW signals of AIC and rotating massive star iron core
collapse and find that they can be distinguished, but only if the distance to the source is known and a
detailed reconstruction of the GW time series from detector data is possible. Some of our AIC models
form massive quasi-Keplerian accretion disks after bounce. The disk mass is very sensitive to progenitor
mass and angular momentum distribution. In rapidly differentially rotating models whose precollapse
masses are significantly larger than the Chandrasekhar mass, the resulting disk mass can be as large as
0:8M. Slowly and/or uniformly rotating models that are limited to masses near the Chandrasekhar
mass produce much smaller disks or no disk at all. Finally, we find that the postbounce cores of rapidly
spinning white dwarfs can reach sufficiently rapid rotation to develop a gravitorotational bar-mode
instability. Moreover, many of our models exhibit sufficiently rapid and differential rotation to become
subject to recently discovered low-E_(rot)/│W│-type dynamical instabilities