68 research outputs found
Prospects for joint gravitational-wave and electromagnetic observations of neutron-star--black-hole coalescing binaries
Coalescing neutron-star-black-hole (NS-BH) binaries are a promising source of
gravitational-wave (GW) signals detectable with large-scale laser
interferometers such as Advanced LIGO and Virgo. They are also one of the main
short gamma-ray burst (SGRB) progenitor candidates. If the BH tidally disrupts
its companion, an SGRB may be ignited when a sufficiently massive accretion
disk forms around the remnant BH. Detecting an NS-BH coalescence both in the GW
and electromagnetic (EM) spectrum offers a wealth of information about the
nature of the source. How much can actually be inferred from a joint detection
is unclear, however, as a mass/spin degeneracy may reduce the GW measurement
accuracy. To shed light on this problem and on the potential of joint EM+GW
observations, we here combine recent semi-analytical predictions for the
remnant disk mass with estimates of the parameter-space portion that is
selected by a GW detection. We identify cases in which an SGRB ignition is
supported, others in which it can be excluded, and finally others in which the
outcome depends on the chosen model for the currently unknown NS equation of
state. We pinpoint a range of systems that would allow us to place lower bounds
on the equation of state stiffness if both the GW emission and its EM
counterpart are observed. The methods we develop can broaden the scope of
existing GW detection and parameter-estimation algorithms and could allow us to
disregard about half of the templates in an NS-BH search following an SGRB
trigger, increasing its speed and sensitivity.Comment: 5 pages, 3 figures; matches published versio
Distinguishing compact binary population synthesis models using gravitational-wave observations of coalescing binary black holes
The coalescence of compact binaries containing neutron stars or black holes
is one of the most promising signals for advanced ground-based laser
interferometer gravitational-wave detectors, with the first direct detections
expected over the next few years. The rate of binary coalescences and the
distribution of component masses is highly uncertain, and population synthesis
models predict a wide range of plausible values. Poorly constrained parameters
in population synthesis models correspond to poorly understood astrophysics at
various stages in the evolution of massive binary stars, the progenitors of
binary neutron star and binary black hole systems. These include effects such
as supernova kick velocities, parameters governing the energetics of common
envelope evolution and the strength of stellar winds. Observing multiple binary
black hole systems through gravitational waves will allow us to infer details
of the astrophysical mechanisms that lead to their formation. Here we simulate
gravitational-wave observations from a series of population synthesis models
including the effects of known selection biases, measurement errors and
cosmology. We compare the predictions arising from different models and show
that we will be able to distinguish between them with observations (or the lack
of them) from the early runs of the advanced LIGO and Virgo detectors. This
will allow us to narrow down the large parameter space for binary evolution
models.Comment: 16 pages, 8 figures, updated to match version published in Ap
Analytical meets numerical relativity - status of complete gravitational waveform models for binary black holes
Models of gravitational waveforms from coalescing black-hole binaries play a
crucial role in the efforts to detect and interpret the signatures of those
binaries in the data of large-scale interferometers. Here we summarize recent
models that combine information both from analytical approximations and
numerical relativity. We briefly lay out and compare the strategies employed to
build such complete models and we recapitulate the errors associated with
various aspects of the modelling process.Comment: 13 pages, 2 figures, 1 table, NRDA2011/Amaldi 9 proceedings;
published version with extended discussion of accuracy requirements and a new
figure
Towards models of gravitational waveforms from generic binaries II: Modelling precession effects with a single effective precession parameter
Gravitational waves (GWs) emitted by generic black-hole binaries show a rich
structure that directly reflects the complex dynamics introduced by the
precession of the orbital plane, which poses a real challenge to the
development of generic waveform models. Recent progress in modelling these
signals relies on an approximate decoupling between the non-precessing secular
inspiral and a precession-induced rotation. However, the latter depends in
general on all physical parameters of the binary which makes modelling efforts
as well as understanding parameter-estimation prospects prohibitively complex.
Here we show that the dominant precession effects can be captured by a reduced
set of spin parameters. Specifically, we introduce a single \emph{effective
precession spin} parameter, , which is defined from the spin components
that lie in the orbital plane at some (arbitrary) instant during the inspiral.
We test the efficacy of this parameter by considering binary inspiral
configurations specified by the physical parameters of a corresponding
non-precessing-binary configuration (total mass, mass ratio, and spin
components (anti-)parallel to the orbital angular momentum), plus the effective
precession spin applied to the larger black hole. We show that for an
overwhelming majority of random precessing configurations, the precession
dynamics during the inspiral are well approximated by our equivalent
configurations. Our results suggest that in the comparable-mass regime waveform
models with only three spin parameters faithfully represent generic waveforms,
which has practical implications for the prospects of GW searches, parameter
estimation and the numerical exploration of the precessing-binary parameter
space.Comment: 19 pages, 15 figures. Modified discussio
Phenomenological model for the gravitational-wave signal from precessing binary black holes with two-spin effects
The properties of compact binaries, such as masses and spins, are imprinted
in the gravitational-waves they emit and can be measured using parameterised
waveform models. Accurately and efficiently describing the complicated
precessional dynamics of the various angular momenta of the system in these
waveform models is the object of active investigation. One of the key models
extensively used in the analysis of LIGO and Virgo data is the
single-precessing-spin waveform model IMRPhenomPv2. In this article we present
a new model IMRPhenomPv3 which includes the effects of two independent spins in
the precession dynamics. Whereas IMRPhenomPv2 utilizes a single-spin
frequency-dependent post-Newtonian rotation to describe precession effects, the
improved model, IMRPhenomPv3, employs a double-spin rotation that is based on
recent developments in the description of precessional dynamics. Besides
double-spin precession, the improved model benefits from a more accurate
description of precessional effects. We validate our new model against a large
set of precessing numerical-relativity simulations. We find that IMRPhenomPv3
has better agreement with the inspiral portion of precessing binary-black-hole
simulations and is more robust across a larger region of the parameter space
than IMRPhenomPv2. As a first application we analyse, for the first time, the
gravitational-wave event GW151226 with a waveform model that describes two-spin
precession. Within statistical uncertainty our results are consistent with
published results. IMRPhenomPv3 will allow studies of the measurability of
individual spins of binary black holes using GWs and can be used as a
foundation upon which to build further improvements, such as modeling
precession through merger, extending to higher multipoles, and including tidal
effects.Comment: 15 pages, 5 figure
Numerical Inside View of Hypermassive Remnant Models for GW170817
The first multimessenger observation attributed to a merging neutron star
binary provided an enormous amount of observational data. Unlocking the full
potential of this data requires a better understanding of the merger process
and the early post-merger phase, which are crucial for the later evolution that
eventually leads to observable counterparts. In this work, we perform standard
hydrodynamical numerical simulations of a system compatible with GW170817. We
focus on a single equation of state (EOS) and two mass ratios, while neglecting
magnetic fields and neutrino radiation. We then apply newly developed
postprocessing and visualization techniques to the results obtained for this
basic setting. The focus lies on understanding the three-dimensional structure
of the remnant, most notably the fluid flow pattern, and its evolution until
collapse. We investigate the evolution of mass and angular momentum
distribution up to collapse, as well as the differential rotation along and
perpendicular to the equatorial plane. For the cases that we studied, the
remnant cannot be adequately modeled as a differentially rotating axisymetric
NS. Further, the dominant aspect leading to collapse is the GW radiation and
not internal redistribution of angular momentum. We relate features of the
gravitational wave signal to the evolution of the merger remnant, and make the
waveforms publicly available. Finally, we find that the three-dimensional
vorticity field inside the disk is dominated by medium-scale perturbances and
not the orbital velocity, with potential consequences for magnetic field
amplification effects.Comment: 20 pages, 17 figure
Inconsistent black hole kick estimates from gravitational-wave models
The accuracy of gravitational-wave models of compact binaries has
traditionally been addressed by the mismatch between the model and
numerical-relativity simulations. This is a measure of the overall agreement
between the two waveforms. However, the largest modelling error typically
appears in the strong-field merger regime and may affect subdominant signal
harmonics more strongly. These inaccuracies are often not well characterised by
the mismatch. We explore the use of a complementary, physically motivated tool
to investigate the accuracy of gravitational-wave harmonics in waveform models:
the remnant's recoil, or kick velocity. Asymmetric binary mergers produce
remnants with significant recoil, encoded by subtle imprints in the
gravitational-wave signal. The kick estimate is highly sensitive to the
intrinsic inaccuracies of the modelled gravitational-wave harmonics during the
strongly relativistic merger regime. Here we investigate the accuracy of the
higher harmonics in four state-of-the-art waveform models of binary black
holes. We find that the SEOBNRv4HM_ROM, IMRPhenomHM, IMRPhenomXHM and
NRHybSur3dq8 models are not consistent in their kick predictions. Our results
enable us to identify regions in the parameter space where the models require
further improvement and support the use of the kick estimate to investigate
waveform systematics. We discuss how numerical-relativity kick estimates could
be used to calibrate waveform models further, proposing the first steps towards
kick-based gravitational-wave tuning.Comment: 31 pages, 17 figure
Simulations of black-hole binaries with unequal masses or non-precessing spins: accuracy, physical properties, and comparison with post-Newtonian results
We present gravitational waveforms for the last orbits and merger of
black-hole-binary (BBH) systems along two branches of the BBH parameter space:
equal-mass binaries with equal non-precessing spins, and nonspinning
unequal-mass binaries. The waveforms are calculated from numerical solutions of
Einstein's equations for black-hole binaries that complete between six and ten
orbits before merger. Along the equal-mass spinning branch, the spin parameter
of each BH is , and along the unequal-mass
branch the mass ratio is . We discuss the construction of
low-eccentricity puncture initial data for these cases, the properties of the
final merged BH, and compare the last 8-10 GW cycles up to with
the phase and amplitude predicted by standard post-Newtonian (PN) approximants.
As in previous studies, we find that the phase from the 3.5PN TaylorT4
approximant is most accurate for nonspinning binaries. For equal-mass spinning
binaries the 3.5PN TaylorT1 approximant (including spin terms up to only 2.5PN
order) gives the most robust performance, but it is possible to treat TaylorT4
in such a way that it gives the best accuracy for spins . When
high-order amplitude corrections are included, the PN amplitude of the
modes is larger than the NR amplitude by between 2-4%.Comment: 21 pages, 9 figures, 6 tables. Version accepted by PR
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