969 research outputs found
Localization of short duration gravitational-wave transients with the early advanced LIGO and Virgo detectors
The Laser Interferometer Gravitational wave Observatory (LIGO) and Virgo,
advanced ground-based gravitational-wave detectors, will begin collecting
science data in 2015. With first detections expected to follow, it is important
to quantify how well generic gravitational-wave transients can be localized on
the sky. This is crucial for correctly identifying electromagnetic counterparts
as well as understanding gravitational-wave physics and source populations. We
present a study of sky localization capabilities for two search and parameter
estimation algorithms: \emph{coherent WaveBurst}, a constrained likelihood
algorithm operating in close to real-time, and \emph{LALInferenceBurst}, a
Markov chain Monte Carlo parameter estimation algorithm developed to recover
generic transient signals with latency of a few hours. Furthermore, we focus on
the first few years of the advanced detector era, when we expect to only have
two (2015) and later three (2016) operational detectors, all below design
sensitivity. These detector configurations can produce significantly different
sky localizations, which we quantify in detail. We observe a clear improvement
in localization of the average detected signal when progressing from
two-detector to three-detector networks, as expected. Although localization
depends on the waveform morphology, approximately 50% of detected signals would
be imaged after observing 100-200 deg in 2015 and 60-110 deg in 2016,
although knowledge of the waveform can reduce this to as little as 22 deg.
This is the first comprehensive study on sky localization capabilities for
generic transients of the early network of advanced LIGO and Virgo detectors,
including the early LIGO-only two-detector configuration.Comment: 18 pages, 8 figure
An information-theoretic approach to the gravitational-wave burst detection problem
The observational era of gravitational-wave astronomy began in the Fall of
2015 with the detection of GW150914. One potential type of detectable
gravitational wave is short-duration gravitational-wave bursts, whose waveforms
can be difficult to predict. We present the framework for a new detection
algorithm for such burst events -- \textit{oLIB} -- that can be used in
low-latency to identify gravitational-wave transients independently of other
search algorithms. This algorithm consists of 1) an excess-power event
generator based on the Q-transform -- \textit{Omicron} --, 2) coincidence of
these events across a detector network, and 3) an analysis of the coincident
events using a Markov chain Monte Carlo Bayesian evidence calculator --
\textit{LALInferenceBurst}. These steps compress the full data streams into a
set of Bayes factors for each event; through this process, we use elements from
information theory to minimize the amount of information regarding the
signal-versus-noise hypothesis that is lost. We optimally extract this
information using a likelihood-ratio test to estimate a detection significance
for each event. Using representative archival LIGO data, we show that the
algorithm can detect gravitational-wave burst events of astrophysical strength
in realistic instrumental noise across different burst waveform morphologies.
We also demonstrate that the combination of Bayes factors by means of a
likelihood-ratio test can improve the detection efficiency of a
gravitational-wave burst search. Finally, we show that oLIB's performance is
robust against the choice of gravitational-wave populations used to model the
likelihood-ratio test likelihoods
Gravitational Wave Burst Source Direction Estimation using Time and Amplitude Information
In this article we study two problems that arise when using timing and
amplitude estimates from a network of interferometers (IFOs) to evaluate the
direction of an incident gravitational wave burst (GWB). First, we discuss an
angular bias in the least squares timing-based approach that becomes
increasingly relevant for moderate to low signal-to-noise ratios. We show how
estimates of the arrival time uncertainties in each detector can be used to
correct this bias. We also introduce a stand alone parameter estimation
algorithm that can improve the arrival time estimation and provide
root-sum-squared strain amplitude (hrss) values for each site. In the second
part of the paper we discuss how to resolve the directional ambiguity that
arises from observations in three non co-located interferometers between the
true source location and its mirror image across the plane containing the
detectors. We introduce a new, exact relationship among the hrss values at the
three sites that, for sufficiently large signal amplitudes, determines the true
source direction regardless of whether or not the signal is linearly polarized.
Both the algorithm estimating arrival times, arrival time uncertainties, and
hrss values and the directional follow-up can be applied to any set of
gravitational wave candidates observed in a network of three non co-located
interferometers. As a case study we test the methods on simulated waveforms
embedded in simulations of the noise of the LIGO and Virgo detectors at design
sensitivity.Comment: 10 pages, 14 figures, submitted to PR
A Coincidence Null Test for Poisson-Distributed Events
When transient events are observed with multiple sensors, it is often
necessary to establish the significance of coincident events. We derive a
universal null test for an arbitrary number of sensors motivated by the
archetypal detection problem for independent Poisson-distributed events in
gravitational-wave detectors such as LIGO and Virgo. In these detectors,
transient events may be witnessed by myriad channels that record
interferometric signals and the surrounding physical environment. We apply our
null test to a broad set of simulated gravitational-wave events as well as to a
real gravitational-wave detection to determine which auxiliary channels do and
do not witness real gravitational waves, and therefore which are safe to use
when constructing vetoes. We also describe how our approach can be used to
study detector artifacts and their origin, as well as to quantify the
statistical independence of candidate GW signals from noise artifacts observed
in auxiliary channels.Comment: 14 pages, 7 Figure
Optimizing Vetoes for Gravitational-wave Transient Searches
Interferometric gravitational-wave detectors like LIGO, GEO600 and Virgo record a surplus of information above and beyond possible gravitational-wave events. These auxiliary channels capture information about the state of the detector and its surroundings which can be used to infer potential terrestrial noise sources of some gravitational-wave-like events. We present an algorithm addressing the ordering (or equivalently optimizing) of such information from auxiliary systems in gravitational-wave detectors to establish veto conditions in searches for gravitational-wave transients. The procedure was used to identify vetoes for searches for unmodelled transients by the LIGO and Virgo collaborations during their science runs from 2005 through 2007. In this work we present the details of the algorithm; we also use a limited amount of data from LIGO's past runs in order to examine the method, compare it with other methods, and identify its potential to characterize the instruments themselves. We examine the dependence of Receiver Operating Characteristic curves on the various parameters of the veto method and the implementation on real data. We find that the method robustly determines important auxiliary channels, ordering them by the apparent strength of their correlations to the gravitational-wave channel. This list can substantially reduce the background of noise events in the gravitational-wave data. In this way it can identify the source of glitches in the detector as well as assist in establishing confidence in the detection of gravitational-wave transients
Observational implications of lowering the LIGO-Virgo alert threshold
The recent detection of the binary-neutron-star merger associated with GW170817 by both the Laser Interferometer Gravitational-Wave Observatory (LIGO) and Virgo and the network of electromagnetic-spectrum observing facilities around the world has made the multi-messenger detection of gravitational-wave (GW) events a reality. These joint detections allow us to probe GW sources in greater detail and provide us with the possibility of confidently establishing events that would not have been detected in GW data alone. In this Letter, we explore the prospects of using the electromagnetic (EM) follow-up of low-significance GW event candidates to increase the sample of confident detections with EM counterparts. We find that the GW-alert threshold change that would roughly double the number of detectable astrophysical events would increase the false-alarm rate (FAR) by more than five orders of magnitude from 1 per 100 years to more than 1000 per year. We find that the localization costs of following up low-significance candidates are marginal, as the same changes to FAR only increase distance/area localizations by less than a factor of 2 and increase volume localization by less than a factor of 4. We argue that EM follow-up thresholds for low-significance candidates should be set on the basis of alert purity (P_(astro)) and not FAR. Ideally, such estimates of P_(astro) would be provided by LIGO-Virgo, but in their absence we provide estimates of the average purity of the GW candidate alerts issued by LIGO-Virgo as a function of FAR for various LIGO-Virgo observing epochs
Noise Reduction in Gravitational-wave Data via Deep Learning
With the advent of gravitational wave astronomy, techniques to extend the reach of gravitational wave detectors are desired. In addition to the stellar-mass black hole and neutron star mergers already detected, many more are below the surface of the noise, available for detection if the noise is reduced enough. Our method (DeepClean) applies machine learning algorithms to gravitational wave detector data and data from on-site sensors monitoring the instrument to reduce the noise in the time-series due to instrumental artifacts and environmental contamination. This framework is generic enough to subtract linear, non-linear, and non-stationary coupling mechanisms. It may also provide handles in learning about the mechanisms which are not currently understood to be limiting detector sensitivities. The robustness of the noise reduction technique in its ability to efficiently remove noise with no unintended effects on gravitational-wave signals is also addressed through software signal injection and parameter estimation of the recovered signal. It is shown that the optimal SNR ratio of the injected signal is enhanced by ∼21.6% and the recovered parameters are consistent with the injected set. We present the performance of this algorithm on linear and non-linear noise sources and discuss its impact on astrophysical searches by gravitational wave detectors
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