30 research outputs found
A unified approach to discriminators for searches of gravitational waves from compact binary coalescences
We describe a general mathematical framework for discriminators in
the context of the compact binary coalescence search. We show that with any
is associated a vector bundle over the signal manifold, that is, the
manifold traced out by the signal waveforms in the function space of data
segments. The is then defined as the square of the norm of the
data vector projected onto a finite dimensional subspace (the fibre) of the
Hilbert space of data trains and orthogonal to the signal waveform - any such
fibre leads to a discriminator and the full vector bundle comprising
the subspaces and the base manifold constitute the discriminator. We
show that the discriminators used so far in the CBC searches
correspond to different fiber structures constituting different vector bundles
on the same base manifold, namely, the parameter space. The general formulation
indicates procedures to formulate new s which could be more effective
in discriminating against commonly occurring glitches in the data. It also
shows that no with a reasonable degree of freedom is foolproof. It
could also shed light on understanding why the traditional works so
well. As an example, we propose a family of ambiguity discriminators
that is an alternative to the traditional one. Any such ambiguity
makes use of the filtered output of the template bank, thus adding negligible
cost to the overall search. We test the performance of ambiguity on
simulated data using spinless TaylorF2 waveforms. We show that the ambiguity
essentially gives a clean separation between glitches and signals.
Finally, we investigate the effects of mismatch between signal and templates on
the and also further indicate how the ambiguity can be
generalized to detector networks for coherent observations.Comment: 21 pages, 5 figure, abstract is shortened to comply with the arXiv's
1920 characters limitation, v2: accepted for publication in PR
Gravitational-wave template banks for novel compact binaries
We introduce a novel method to generate a bank of gravitational-waveform
templates of binary black hole (BBH) mergers for matched-filter searches in
LIGO, Virgo and Kagra data.We derive a novel expression for the metric
approximation to the distance between templates, which is suitable for
precessing BBHs and/or systems with higher-order modes (HM) imprints and we use
it to meaningfully define a template probability density across the parameter
space. We employ a masked autoregressive normalizing flow model which can be
conveniently trained to quickly reproduce the target probability distribution
and sample templates from it. Thanks to the normalizing flow, our code takes a
few {\it hours} to produce random template banks with millions of templates,
making it particularly suitable for high-dimensional spaces, such as those
associated to precession, eccentricity and/or HM. After validating the
performance of our method, we generate a bank for precessing black holes and a
bank for aligned-spin binaries with HMs: with only 5% of the injections with
fitting factor below the target of 0.97, we show that both banks cover
satisfactorily the space. Our publicly released code mbank will enable searches
of high-dimensional regions of BBH signal space, hitherto unfeasible due to the
prohibitive cost of bank generation
An optimal method for scheduling observations of large sky error regions for finding optical counterparts to transients
The discovery and subsequent study of optical counterparts to transient
sources is crucial for their complete astrophysical understanding. Various
gamma ray burst (GRB) detectors, and more notably the ground--based
gravitational wave detectors, typically have large uncertainties in the sky
positions of detected sources. Searching these large sky regions spanning
hundreds of square degrees is a formidable challenge for most ground--based
optical telescopes, which can usually image less than tens of square degrees of
the sky in a single night. We present algorithms for optimal scheduling of such
follow--up observations in order to maximize the probability of imaging the
optical counterpart, based on the all--sky probability distribution of the
source position. We incorporate realistic observing constraints like the
diurnal cycle, telescope pointing limitations, available observing time, and
the rising/setting of the target at the observatory location. We use
simulations to demonstrate that our proposed algorithms outperform the default
greedy observing schedule used by many observatories. Our algorithms are
applicable for follow--up of other transient sources with large positional
uncertainties, like Fermi--detected GRBs, and can easily be adapted for
scheduling radio or space--based X--ray followup.Comment: Submitted to ApJ. 18 pages, 15 figure
Hierarchical search for compact binary coalescences in the Advanced LIGO's first two observing runs
Detection of many compact binary coalescences (CBCs) is one of the primary
goals of the present and future ground-based gravitational-wave (GW) detectors.
While increasing the detectors' sensitivities will be crucial in achieving
this, efficient data analysis strategies can play a vital role. With given
computational power in hand, efficient data analysis techniques can expand the
size and dimensionality of the parameter space to search for a variety of GW
sources. Matched filtering based analyses that depend on modeled signals to
produce adequate signal-to-noise ratios for signal detection may miss them if
the parameter space is too restrained. Specifically, the CBC search is
currently limited to non-precessing binaries only, where the spins of the
components are either aligned or anti-aligned to the orbital angular momentum.
A hierarchical search for CBCs is thus well motivated. The first stage of this
search is performed by matched filtering coarsely sampled data with a coarse
template bank to look for candidate events. These candidates are then followed
up for a finer search around the vicinity of an event's parameter space.
Performing such a search leads to enormous savings in computational cost. Here
we report the first successful implementation of the hierarchical search as a
PyCBC-based production pipeline to perform a complete analysis of LIGO
observing runs. With this, we analyze Advanced LIGO's first and second
observing run data. We recover all the events detected by the PyCBC (flat)
search in the first GW catalog, GWTC-1, published by the LIGO-Virgo
collaboration, with nearly the same significance using a scaled background. In
the analysis, we get an impressive factor of 20 speed-up in computation
compared to the flat search. With a standard injection study, we show that the
sensitivity of the hierarchical search remains comparable to the flat search
within the error bars.Comment: 13 pages, 8 figure
Detection and characterization of spin-orbit resonances in the advanced gravitational wave detectors era
In this paper, we test the performance of templates in detection and
characterization of Spin-orbit resonant (SOR) binaries. We use precessing
SEOBNRv3 waveforms as well as {\it four} numerical relativity (NR) waveforms to
model GWs from SOR binaries and filter them through IMRPhenomD, SEOBNRv4
(non-precessing) and IMRPhenomPv2 (precessing) approximants. We find that
IMRPhenomD and SEOBNRv4 recover only of injections with fitting
factor (FF) higher than 0.97 (or 90\% of injections with ).However, using the sky-maxed statistic, IMRPhenomPv2 performs
magnificently better than their non-precessing counterparts with recovering
of the injections with FFs higher than 0.97. Interestingly, injections
with have higher FFs ( is the angle
between the components of the black hole spins in the plane orthogonal to the
orbital angular momentum) as compared to their and
generic counterparts. This implies that we will have a slight observation bias
towards SORs while using non-precessing templates for
searches. All template approximants are able to recover most of the injected NR
waveforms with FFs . For all the injections including NR, the error in
estimating chirp mass remains below with minimum error for resonant binaries. The symmetric mass ratio can be estimated
with errors below . The effective spin parameter is
measured with maximum absolute error of 0.13. The in-plane spin parameter
is mostly underestimated indicating that a precessing signal will be
recovered as a relatively less precessing signal. Based on our findings, we
conclude that we not only need improvements in waveform models towards
precession and non-quadrupole modes but also better search strategies for
precessing GW signals.Comment: 27 pages, 15 figures. Abstract shortened due to word limi
Detection and characterization of spin-orbit resonances in the advanced gravitational wave detectors era
Spin-orbit resonances have important astrophysical implications as the evolution and subsequent coalescence of supermassive black hole binaries in one of these configurations may lead to low recoil velocity of merger remnants. It has also been shown that black hole spins in comparable mass stellar-mass black hole binaries could preferentially lie in a resonant plane when their gravitational waves (GWs) enter the advanced LIGO frequency band [1]. Therefore, it is highly desirable to investigate the possibility of detection and subsequent characterization of such GW sources in the advanced detector era, which can, in turn, improve our perception of their high mass counterparts. The current detection pipelines involve only nonprecessing templates for compact binary searches whereas parameter estimation pipelines can afford to use approximate precessing templates. In this paper, we test the performance of these templates in detection and characterization of spin-orbit resonant binaries. We use fully precessing time-domain SEOBNRv3 waveforms as well as four numerical relativity (NR) waveforms to model GWs from spin-orbit resonant binaries and filter them through IMRPhenomD, SEOBNRv4 and IMRPhenomPv2 approximants. We find that the nonprecessing approximants IMRPhenomD and SEOBNRv4 recover only ∼70% of injections with fitting factor (FF) higher than 0.97 (or 90% of injections with FF>0.9). This loss in signal-to-noise ratio is mainly due to the missing physics in these approximants in terms of precession and nonquadrupole modes. However, if we use a new statistic, i.e., maximizing the matched filter output over the sky-location parameters as well, the precessing approximant IMRPhenomPv2 performs magnificently better than their nonprecessing counterparts with recovering 99% of the injections with FFs higher than 0.97. Interestingly, injections with Δϕ=180° have higher FFs (Δϕ is the angle between the components of the black hole spins in the plane orthogonal to the orbital angular momentum) as compared to their Δϕ=0° and generic counterparts. This is because Δϕ=180° binaries are not as strongly precessing as Δϕ=0° and generic binaries. This implies that we will have a slight observation bias towards Δϕ=180° and away from Δϕ=0° resonant binaries while using nonprecessing templates for searches. Moreover, all template approximants are able to recover most of the injected NR waveforms with FFs >0.95. For all the injections including NR, the systematic error in estimating chirp mass remains below <10% with minimum error for Δϕ=180° resonant binaries. The symmetric mass-ratio can be estimated with errors below 15%. The effective spin parameter χ_(eff) is measured with maximum absolute error of 0.13. The in-plane spin parameter χ_p is mostly underestimated indicating that a precessing signal will be recovered as a relatively less precessing signal. Based on our findings, we conclude that we not only need improvements in waveform models towards precession and nonquadrupole modes but also better search strategies for precessing GW signals
Search for gravitational-lensing signatures in the full third observing run of the LIGO-Virgo network
Gravitational lensing by massive objects along the line of sight to the source causes distortions of gravitational wave-signals; such distortions may reveal information about fundamental physics, cosmology and astrophysics. In this work, we have extended the search for lensing signatures to all binary black hole events from the third observing run of the LIGO--Virgo network. We search for repeated signals from strong lensing by 1) performing targeted searches for subthreshold signals, 2) calculating the degree of overlap amongst the intrinsic parameters and sky location of pairs of signals, 3) comparing the similarities of the spectrograms amongst pairs of signals, and 4) performing dual-signal Bayesian analysis that takes into account selection effects and astrophysical knowledge. We also search for distortions to the gravitational waveform caused by 1) frequency-independent phase shifts in strongly lensed images, and 2) frequency-dependent modulation of the amplitude and phase due to point masses. None of these searches yields significant evidence for lensing. Finally, we use the non-detection of gravitational-wave lensing to constrain the lensing rate based on the latest merger-rate estimates and the fraction of dark matter composed of compact objects