310 research outputs found
Inferences about supernova physics from gravitational-wave measurements: GW151226 spin misalignment as an indicator of strong black-hole natal kicks
The inferred parameters of the binary black hole GW151226 are consistent with
nonzero spin for the most massive black hole, misaligned from the binary's
orbital angular momentum. If the black holes formed through isolated binary
evolution from an initially aligned binary star, this misalignment would then
arise from a natal kick imparted to the first-born black hole at its birth
during stellar collapse. We use simple kinematic arguments to constrain the
characteristic magnitude of this kick, and find that a natal kick km/s must be imparted to the black hole at birth to produce misalignments
consistent with GW151226. Such large natal kicks exceed those adopted by
default in most of the current supernova and binary evolution models.Comment: 6 pages, 2 figures. Accepted for publication in PRL. Selected in
physics.aps.or
An architecture for efficient gravitational wave parameter estimation with multimodal linear surrogate models
The recent direct observation of gravitational waves has further emphasized
the desire for fast, low-cost, and accurate methods to infer the parameters of
gravitational wave sources. Due to expense in waveform generation and data
handling, the cost of evaluating the likelihood function limits the
computational performance of these calculations. Building on recently developed
surrogate models and a novel parameter estimation pipeline, we show how to
quickly generate the likelihood function as an analytic, closed-form
expression. Using a straightforward variant of a production-scale parameter
estimation code, we demonstrate our method using surrogate models of
effective-one-body and numerical relativity waveforms. Our study is the first
time these models have been used for parameter estimation and one of the first
ever parameter estimation calculations with multi-modal numerical relativity
waveforms, which include all l <= 4 modes. Our grid-free method enables rapid
parameter estimation for any waveform with a suitable reduced-order model. The
methods described in this paper may also find use in other data analysis
studies, such as vetting coincident events or the computation of the
coalescing-compact-binary detection statistic.Comment: 10 pages, 3 figures, and 1 tabl
Testing gravitational parity violation with coincident gravitational waves and short gamma-ray bursts
Gravitational parity violation is a possibility motivated by particle
physics, string theory and loop quantum gravity. One effect of it is amplitude
birefringence of gravitational waves, whereby left and right
circularly-polarized waves propagate at the same speed but with different
amplitude evolution. Here we propose a test of this effect through coincident
observations of gravitational waves and short gamma-ray bursts from binary
mergers involving neutron stars. Such gravitational waves are highly left or
right circularly-polarized due to the geometry of the merger. Using
localization information from the gamma-ray burst, ground-based gravitational
wave detectors can measure the distance to the source with reasonable accuracy.
An electromagnetic determination of the redshift from an afterglow or host
galaxy yields an independent measure of this distance. Gravitational parity
violation would manifest itself as a discrepancy between these two distance
measurements. We exemplify such a test by considering one specific effective
theory that leads to such gravitational parity-violation, Chern-Simons gravity.
We show that the advanced LIGO-Virgo network and all-sky gamma-ray telescopes
can be sensitive to the propagating sector of Chern-Simons gravitational parity
violation to a level roughly two orders of magnitude better than current
stationary constraints from the LAGEOS satellites.Comment: 21 pages, 2 figures, submitted to Phys. Rev.
A more effective coordinate system for parameter estimation of precessing compact binaries from gravitational waves
Ground-based gravitational wave detectors are sensitive to a narrow range of
frequencies, effectively taking a snapshot of merging compact-object binary
dynamics just before merger. We demonstrate that by adopting analysis
parameters that naturally characterize this 'picture', the physical parameters
of the system can be extracted more efficiently from the gravitational wave
data, and interpreted more easily. We assess the performance of MCMC parameter
estimation in this physically intuitive coordinate system, defined by (a) a
frame anchored on the binary's spins and orbital angular momentum and (b) a
time at which the detectors are most sensitive to the binary's gravitational
wave emission. Using anticipated noise curves for the advanced-generation LIGO
and Virgo gravitational wave detectors, we find that this careful choice of
reference frame and reference time significantly improves parameter estimation
efficiency for BNS, NS-BH, and BBH signals.Comment: 11 pages, 5 figures, submitted to Phys. Rev.
Asymptotic frame selection for binary black hole spacetimes II: Post-Newtonian limit
One way to select a preferred frame from gravitational radiation is via the
principal axes of , an average of the action of rotation group generators
on the Weyl tensor at asymptotic infinity. In this paper we evaluate this
time-domain average for a quasicircular binary using approximate
(post-Newtonian) waveforms. For nonprecessing unequal-mass binaries, we show
the dominant eigenvector of this tensor lies along the orbital angular
momentum. For precessing binaries, this frame is not generally aligned with
either the orbital or total angular momentum, working to leading order in the
spins. The difference between these two quantities grows with time, as the
binary approaches the end of the inspiral and both precession and higher
harmonics become more significant.Comment: 12 pages, 4 figure
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