279 research outputs found
Finding diamonds in the rough: Targeted Sub-threshold Search for Strongly-lensed Gravitational-wave Events
Strong gravitational lensing of gravitational waves can produce duplicate
signals separated in time with different amplitudes. We consider the case in
which strong lensing produces identifiable gravitational-wave events and weaker
sub-threshold signals hidden in the noise background. We present a search
method for the sub-threshold signals using reduced template banks targeting
specific confirmed gravitational-wave events. We apply the method to all events
from Advanced LIGO's first and second observing run O1/O2. Using GW150914 as an
example, we show that the method effectively reduces the noise background and
raises the significance of (near-) sub-threshold triggers. In the case of
GW150914, we can improve the sensitive distance by . Finally,
we present the top possible lensed candidates for O1/O2 gravitational-wave
events that passed our nominal significance threshold of False-Alarm-Rate days
Targeted Sub-threshold Search for Strongly-lensed Gravitational-wave Events
Strong gravitational lensing of gravitational waves can produce duplicated signals that are separated in time and with different amplitudes. We consider the case in which strong lensing produces identifiable gravitational-wave events together with weaker sub-threshold signals that are hidden in the noise background. We present a search method for the sub-threshold signals using reduced template banks targeting specific confirmed gravitational-wave events. We apply the method to an event from Advanced LIGO's first observing run O1, GW151012. We show that the method is effective in reducing the noise background and hence raising the significance of (near-) sub-threshold triggers. In the case of GW151012, we are able to improve the sensitive distance by 10%−25%. Finally, we present the 10 most significant events for GW151012-like signals in O1. Besides the already confirmed gravitational-wave detections, none of the candidates pass our nominal significance threshold of False-Alarm-Rate ≤ 1/30 days
TESLA-X: An effective method to search for sub-threshold lensed gravitational waves with a targeted population model
Strong gravitational lensing can produce copies of gravitational-wave signals
from the same source with the same waveform morphologies but different
amplitudes and arrival times. Some of these strongly-lensed gravitational-wave
signals can be demagnified and become sub-threshold. We present TESLA-X, an
enhanced approach to the original GstLAL-based TargetEd Subthreshold Lensing
seArch (TESLA) method, for improving the detection efficiency of these
potential sub-threshold lensed signals. TESLA-X utilizes lensed injections to
generate a targeted population model and a targeted template bank. We compare
the performance of a full template bank search, TESLA, and TESLA-X methods via
a simulation campaign, and demonstrate the performance of TESLA-X in recovering
lensed injections, particularly targeting a mock event. Our results show that
the TESLA-X method achieves a maximum of higher search sensitivity
compared to the TESLA method within the sub-threshold regime, presenting a step
towards detecting the first lensed gravitational wave. TESLA-X will be employed
for the LIGO-Virgo-KAGRA's collaboration-wide analysis to search for lensing
signatures in the fourth observing run
Follow-up analyses to the O3 LIGO-Virgo-KAGRA lensing searches
Along their path from source to observer, gravitational waves may be
gravitationally lensed by massive objects. This results in distortions of the
observed signal which can be used to extract new information about fundamental
physics, astrophysics, and cosmology. Searches for these distortions amongst
the observed signals from the current detector network have already been
carried out, though there have as yet been no confident detections. However,
predictions of the observation rate of lensing suggest detection in the future
is a realistic possibility. Therefore, preparations need to be made to
thoroughly investigate the candidate lensed signals. In this work, we present
some of the follow-up analyses and strategies that could be applied to assess
the significance of such events and ascertain what information may be extracted
about the lens-source system from such candidate signals by applying them to a
number of O3 candidate events, even if these signals did not yield a high
significance for any of the lensing hypotheses. For strongly-lensed candidates,
we verify their significance using a background of simulated unlensed events
and statistics computed from lensing catalogs. We also look for potential
electromagnetic counterparts. In addition, we analyse in detail a candidate for
a strongly-lensed sub-threshold counterpart that is identified by a new method.
For microlensing candidates, we perform model selection using a number of lens
models to investigate our ability to determine the mass density profile of the
lens and constrain the lens parameters. We also look for millilensing
signatures in one of the lensed candidates. Applying these additional analyses
does not lead to any additional evidence for lensing in the candidates that
have been examined. However, it does provide important insight into potential
avenues to deal with high-significance candidates in future observations.Comment: 34 pages, 27 figure
Electromagnetic signatures of far-field gravitational radiation in the 1+3 approach
Gravitational waves from astrophysical sources can interact with background
electromagnetic fields, giving rise to distinctive and potentially detectable
electromagnetic signatures. In this paper, we study such interactions for
far-field gravitational radiation using the 1+3 approach to relativity.
Linearised equations for the electromagnetic field on perturbed Minkowski space
are derived and solved analytically. The inverse Gertsenshtein conversion of
gravitational waves in a static electromagnetic field is rederived, and the
resultant electromagnetic radiation is shown to be significant for highly
magnetised pulsars in compact binary systems. We also obtain a variety of
nonlinear interference effects for interacting gravitational and
electromagnetic waves, although wave-wave resonances previously described in
the literature are absent when the electric-magnetic self-interaction is taken
into account. The fluctuation and amplification of electromagnetic energy flux
as the gravitational wave strength increases towards the
gravitational-electromagnetic frequency ratio is a possible signature of
gravitational radiation from extended astrophysical sources.Comment: Published versio
An Early-warning System for Electromagnetic Follow-up of Gravitational-wave Events
Binary neutron stars (BNSs) will spend ≃10–15 minutes in the band of Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) and Virgo detectors at design sensitivity. Matched-filtering of gravitational-wave (GW) data could in principle accumulate enough signal-to-noise ratio (S/N) to identify a forthcoming event tens of seconds before the companions collide and merge. Here we report on the design and testing of an early-warning GW detection pipeline. Early-warning alerts can be produced for sources that are at low enough redshift so that a large enough S/N accumulates ~10–60 s before merger. We find that about 7% (49%) of the total detectable BNS mergers will be detected 60 s (10 s) before the merger. About 2% of the total detectable BNS mergers will be detected before merger and localized to within 100 deg² (90% credible interval). Coordinated observing by several wide-field telescopes could capture the event seconds before or after the merger. LIGO–Virgo detectors at design sensitivity could facilitate observing at least one event at the onset of merger
Template bank for compact binary mergers in the fourth observing run of Advanced LIGO, Advanced Virgo, and KAGRA
Template banks containing gravitational wave (GW) waveforms are essential for
matched-filtering GW search pipelines. We describe the generation method, the
design, and validation of the template bank used by the GstLAL-based inspiral
pipeline to analyze data from the fourth observing run of LIGO scientific,
Virgo, and KAGRA collaboration. This paper presents a template bank containing
templates that include merging neutron star - neutron star,
neutron star - black hole, and black hole - black hole systems up to a total
mass of . Motivated by observations, component masses below
have dimensionless spins ranging between , while component
masses between to have dimensionless spins ranging between
, where we assume spin-aligned systems. The low-frequency cutoff is
Hz. The templates are placed in the parameter space according to the
metric via a binary tree approach which took
minutes when jobs were parallelized. The template bank generated with this
method has a match or higher for of the injections, thus being as
effective as the template placement method used for the previous observation
runs. The volumes of the templates are computed prior to template placement and
the nearby templates have similar volumes in the coordinate space, henceforth,
enabling a more efficient and less biased implementation of population models.
SVD sorting of the O4 template bank has been renewed to use post-Newtonian
phase terms, which improved the computational efficiency of SVD by nearly times as compared to conventional SVD sorting schemes. Template banks
and searches focusing on the sub-solar mass parameter space and
intermediate-mass black hole parameter space are conducted separately
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