2,685 research outputs found
Enabling high confidence detections of gravitational-wave bursts
With the advanced LIGO and Virgo detectors taking observations the detection
of gravitational waves is expected within the next few years. Extracting
astrophysical information from gravitational wave detections is a well-posed
problem and thoroughly studied when detailed models for the waveforms are
available. However, one motivation for the field of gravitational wave
astronomy is the potential for new discoveries. Recognizing and characterizing
unanticipated signals requires data analysis techniques which do not depend on
theoretical predictions for the gravitational waveform. Past searches for
short-duration un-modeled gravitational wave signals have been hampered by
transient noise artifacts, or "glitches," in the detectors. In some cases, even
high signal-to-noise simulated astrophysical signals have proven difficult to
distinguish from glitches, so that essentially any plausible signal could be
detected with at most 2-3 level confidence. We have put forth the
BayesWave algorithm to differentiate between generic gravitational wave
transients and glitches, and to provide robust waveform reconstruction and
characterization of the astrophysical signals. Here we study BayesWave's
capabilities for rejecting glitches while assigning high confidence to
detection candidates through analytic approximations to the Bayesian evidence.
Analytic results are tested with numerical experiments by adding simulated
gravitational wave transient signals to LIGO data collected between 2009 and
2010 and found to be in good agreement.Comment: 15 pages, 6 figures, submitted to PR
Observing Gravitational Waves with a Single Detector
A major challenge of any search for gravitational waves is to distinguish
true astrophysical signals from those of terrestrial origin. Gravitational-wave
experiments therefore make use of multiple detectors, considering only those
signals which appear in coincidence in two or more instruments. It is unclear,
however, how to interpret loud gravitational-wave candidates observed when only
one detector is operational. In this paper, we demonstrate that the observed
rate of binary black hole mergers can be leveraged in order to make confident
detections of gravitational-wave signals with one detector alone. We quantify
detection confidences in terms of the probability that a signal
candidate is of astrophysical origin. We find that, at current levels of
instrumental sensitivity, loud signal candidates observed with a single
Advanced LIGO detector can be assigned . In the future,
Advanced LIGO may be able to observe single-detector events with confidences
exceeding .Comment: 8 pages, 4 figures; published in CQG; minor updates to match
published versio
Validating gravitational-wave detections: The Advanced LIGO hardware injection system
Hardware injections are simulated gravitational-wave signals added to the Laser Interferometer Gravitational-wave Observatory (LIGO). The detectors’ test masses are physically displaced by an actuator in order to simulate the effects of a gravitational wave. The simulated signal initiates a control-system response which mimics that of a true gravitational wave. This provides an end-to-end test of LIGO’s ability to observe gravitational waves. The gravitational-wave analyses used to detect and characterize signals are exercised with hardware injections. By looking for discrepancies between the injected and recovered signals, we are able to characterize the performance of analyses and the coupling of instrumental subsystems to the detectors’ output channels. This paper describes the hardware injection system and the recovery of injected signals representing binary black hole mergers, a stochastic gravitational wave background, spinning neutron stars, and sine-Gaussians
Enhancing gravitational wave astronomy with galaxy catalogues
Joint gravitational wave (GW) and electromagnetic (EM) observations, as a key
research direction in multi-messenger astronomy, will provide deep insight into
the astrophysics of a vast range of astronomical phenomena. Uncertainties in
the source sky location estimate from gravitational wave observations mean
follow-up observatories must scan large portions of the sky for a potential
companion signal. A general frame of joint GW-EM observations is presented by a
multi-messenger observational triangle. Using a Bayesian approach to
multi-messenger astronomy, we investigate the use of galaxy catalogue and host
galaxy information to reduce the sky region over which follow-up observatories
must scan, as well as study its use for improving the inclination angle
estimates for coalescing binary compact objects. We demonstrate our method
using a simulated neutron stars inspiral signal injected into simulated
Advanced detectors noise and estimate the injected signal sky location and
inclination angle using the Gravitational Wave Galaxy Catalogue. In this case
study, the top three candidates in rank have , and posterior
probability of being the host galaxy, receptively. The standard deviation of
cosine inclination angle (0.001) of the neutron stars binary using
gravitational wave-galaxy information is much smaller than that (0.02) using
only gravitational wave posterior samples.Comment: Proceedings of the Sant Cugat Forum on Astrophysics. 2014 Session on
'Gravitational Wave Astrophysics
Multi-messenger astronomy of gravitational-wave sources with flexible wide-area radio transient surveys
We explore opportunities for multi-messenger astronomy using gravitational
waves (GWs) and prompt, transient low-frequency radio emission to study highly
energetic astrophysical events. We review the literature on possible sources of
correlated emission of gravitational waves and radio transients, highlighting
proposed mechanisms that lead to a short-duration, high-flux radio pulse
originating from the merger of two neutron stars or from a superconducting
cosmic string cusp. We discuss the detection prospects for each of these
mechanisms by low-frequency dipole array instruments such as LWA1, LOFAR and
MWA. We find that a broad range of models may be tested by searching for radio
pulses that, when de-dispersed, are temporally and spatially coincident with a
LIGO/Virgo GW trigger within a \usim 30 second time window and \usim 200
\mendash 500 \punits{deg}^{2} sky region. We consider various possible
observing strategies and discuss their advantages and disadvantages. Uniquely,
for low-frequency radio arrays, dispersion can delay the radio pulse until
after low-latency GW data analysis has identified and reported an event
candidate, enabling a \emph{prompt} radio signal to be captured by a
deliberately targeted beam. If neutron star mergers do have detectable prompt
radio emissions, a coincident search with the GW detector network and
low-frequency radio arrays could increase the LIGO/Virgo effective search
volume by up to a factor of \usim 2. For some models, we also map the
parameter space that may be constrained by non-detections.Comment: 31 pages, 4 figure
Leveraging waveform complexity for confident detection of gravitational waves
The recent completion of Advanced LIGO suggests that gravitational waves may soon be directly observed. Past searches for gravitational-wave transients have been impacted by transient noise artifacts, known as glitches, introduced into LIGO data due to instrumental and environmental effects. In this work, we explore how waveform complexity, instead of signal-to-noise ratio, can be used to rank event candidates and distinguish short duration astrophysical signals from glitches. We test this framework using a new hierarchical pipeline that directly compares the Bayesian evidence of explicit signal and glitch models. The hierarchical pipeline is shown to perform well and, in particular, to allow high-confidence detections of a range of waveforms at a realistic signal-to-noise ratio with a two-detector network
Observations of Giant Pulses from Pulsar PSR B0950+08 using LWA1
We report the detection of giant pulse emission from PSR B0950+08 in 24 hours
of observations made at 39.4 MHz, with a bandwidth of 16 MHz, using the first
station of the Long Wavelength Array, LWA1. We detected 119 giant pulses from
PSR B0950+08 (at its dispersion measure), which we define as having SNRs at
least 10 times larger than for the mean pulse in our data set. These 119 pulses
are 0.035% of the total number of pulse periods in the 24 hours of
observations. The rate of giant pulses is about 5.0 per hour. The cumulative
distribution of pulse strength is a steep power law, , but much less steep than would be expected if we were observing the
tail of a Gaussian distribution of normal pulses. We detected no other
transient pulses in a dispersion measure range from 1 to 90 pc cm, in
the beam tracking PSR B0950+08. The giant pulses have a narrower temporal width
than the mean pulse (17.8 ms, on average, vs. 30.5 ms). The pulse widths are
consistent with a previously observed weak dependence on observing frequency,
which may be indicative of a deviation from a Kolmogorov spectrum of electron
density irregularities along the line of sight. The rate and strength of these
giant pulses is less than has been observed at 100 MHz. Additionally, the
mean (normal) pulse flux density we observed is less than at 100 MHz.
These results suggest this pulsar is weaker and produces less frequent giant
pulses at 39 MHz than at 100 MHz.Comment: 27 pages, 12 figures, typos correcte
Electromagnetic follow-up of gravitational wave transient signal candidates
Pioneering efforts aiming at the development of multi-messenger gravitational
wave and electromagnetic astronomy have been made. An electromagnetic
observation follow-up program of candidate gravitational wave events has been
performed (Dec 17 2009 to Jan 8 2010 and Sep 4 to Oct 20 2010) during the
recent runs of the LIGO and Virgo gravitational wave detectors. It involved
ground-based and space electromagnetic facilities observing the sky at optical,
X-ray and radio wavelengths. The joint gravitational wave and electromagnetic
observation study requires the development of specific image analysis
procedures able to discriminate the possible electromagnetic counterpart of
gravitational wave triggers from contaminant/background events. The paper
presents an overview of the electromagnetic follow-up program and the image
analysis procedures.Comment: Proceedings of the 12th International Conference on "Topics in
Astroparticle and Underground Physics" (TAUP 2011), Munich, September 2011
(to appear in IoP Journal of Physics: Conference Series
Parameter Estimation for Gravitational-wave Bursts with the BayesWave Pipeline
We provide a comprehensive multi-aspect study of the performance of a pipeline used by the LIGO-Virgo Collaboration for estimating parameters of gravitational-wave bursts. We add simulated signals with four different morphologies (sine-Gaussians (SGs), Gaussians, white-noise bursts, and binary black hole signals) to simulated noise samples representing noise of the two Advanced LIGO detectors during their first observing run. We recover them with the BayesWave (BW) pipeline to study its accuracy in sky localization, waveform reconstruction, and estimation of model-independent waveform parameters. BW localizes sources with a level of accuracy comparable for all four morphologies, with the median separation of actual and estimated sky locations ranging from 25 degrees. 1 to 30 degrees. 3. This is a reasonable accuracy in the two-detector case, and is comparable to accuracies of other localization methods studied previously. As BW reconstructs generic transient signals with SG wavelets, it is unsurprising that BW performs best in reconstructing SG and Gaussian waveforms. The BW accuracy in waveform reconstruction increases steeply with the network signal-to-noise ratio (S/N-net), reaching a 85% and 95% match between the reconstructed and actual waveform below S/N-net approximate to 20 and S/N-net approximate to 50, respectively, for all morphologies. The BW accuracy in estimating central moments of waveforms is only limited by statistical errors in the frequency domain, and is also affected by systematic errors in the time domain as BW cannot reconstruct low-amplitude parts of signals that are overwhelmed by noise. The figures of merit we introduce can be used in future characterizations of parameter estimation pipelines
Selective Metal Cation Capture by Soft Anionic Metal-Organic Frameworks via Drastic Single-Crystal-to-Single-Crystal Transformations
In this paper we describe a novel framework for the discovery of the topical
content of a data corpus, and the tracking of its complex structural changes
across the temporal dimension. In contrast to previous work our model does not
impose a prior on the rate at which documents are added to the corpus nor does
it adopt the Markovian assumption which overly restricts the type of changes
that the model can capture. Our key technical contribution is a framework based
on (i) discretization of time into epochs, (ii) epoch-wise topic discovery
using a hierarchical Dirichlet process-based model, and (iii) a temporal
similarity graph which allows for the modelling of complex topic changes:
emergence and disappearance, evolution, and splitting and merging. The power of
the proposed framework is demonstrated on the medical literature corpus
concerned with the autism spectrum disorder (ASD) - an increasingly important
research subject of significant social and healthcare importance. In addition
to the collected ASD literature corpus which we will make freely available, our
contributions also include two free online tools we built as aids to ASD
researchers. These can be used for semantically meaningful navigation and
searching, as well as knowledge discovery from this large and rapidly growing
corpus of literature.Comment: In Proc. Pacific-Asia Conference on Knowledge Discovery and Data
Mining (PAKDD), 201
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