58,247 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
Likelihood-ratio ranking of gravitational-wave candidates in a non-Gaussian background
We describe a general approach to detection of transient gravitational-wave
signals in the presence of non-Gaussian background noise. We prove that under
quite general conditions, the ratio of the likelihood of observed data to
contain a signal to the likelihood of it being a noise fluctuation provides
optimal ranking for the candidate events found in an experiment. The
likelihood-ratio ranking allows us to combine different kinds of data into a
single analysis. We apply the general framework to the problem of unifying the
results of independent experiments and the problem of accounting for
non-Gaussian artifacts in the searches for gravitational waves from compact
binary coalescence in LIGO data. We show analytically and confirm through
simulations that in both cases the likelihood ratio statistic results in an
improved analysis.Comment: 10 pages, 6 figure
A Bayesian method for detecting stellar flares
We present a Bayesian-odds-ratio-based algorithm for detecting stellar flares
in light curve data. We assume flares are described by a model in which there
is a rapid rise with a half-Gaussian profile, followed by an exponential decay.
Our signal model also contains a polynomial background model. This is required
to fit underlying light curve variations that are expected in the data, which
could otherwise partially mimic a flare. We characterise the false alarm
probability and efficiency of this method and compare it with a simpler
thresholding method based on that used in Walkowicz et al (2011). We find our
method has a significant increase in detection efficiency for low
signal-to-noise ratio (S/N) flares. For a conservative false alarm probability
our method can detect 95% of flares with S/N less than ~20, as compared to S/N
of ~25 for the simpler method. As an example we have applied our method to a
selection of stars in Kepler Quarter 1 data. The method finds 687 flaring stars
with a total of 1873 flares after vetos have been applied. For these flares we
have characterised their durations and and signal-to-noise ratios.Comment: Accepted for MNRAS. The code used for the analysis can be found at
https://github.com/BayesFlare/bayesflare/releases/tag/v1.0.
Detecting binary compact-object mergers with gravitational waves: Understanding and Improving the sensitivity of the PyCBC search
We present an improved search for binary compact-object mergers using a
network of ground-based gravitational-wave detectors. We model a volumetric,
isotropic source population and incorporate the resulting distribution over
signal amplitude, time delay, and coalescence phase into the ranking of
candidate events. We describe an improved modeling of the background
distribution, and demonstrate incorporating a prior model of the binary mass
distribution in the ranking of candidate events. We find a and
increase in detection volume for simulated binary neutron star and
neutron star--binary black hole systems, respectively, corresponding to a
reduction of the false alarm rates assigned to signals by between one and two
orders of magnitude.Comment: 7 pages, 3 figures, as accepted by Ap
Real-time filtering and detection of dynamics for compression of HDTV
The preprocessing of video sequences for data compressing is discussed. The end goal associated with this is a compression system for HDTV capable of transmitting perceptually lossless sequences at under one bit per pixel. Two subtopics were emphasized to prepare the video signal for more efficient coding: (1) nonlinear filtering to remove noise and shape the signal spectrum to take advantage of insensitivities of human viewers; and (2) segmentation of each frame into temporally dynamic/static regions for conditional frame replenishment. The latter technique operates best under the assumption that the sequence can be modelled as a superposition of active foreground and static background. The considerations were restricted to monochrome data, since it was expected to use the standard luminance/chrominance decomposition, which concentrates most of the bandwidth requirements in the luminance. Similar methods may be applied to the two chrominance signals
Analysis of Sub-threshold Short Gamma-ray Bursts in Fermi GBM Data
The Fermi Gamma-ray Burst Monitor (GBM) is currently the most prolific
detector of Gamma-Ray Bursts (GRBs). Recently the detection rate of short GRBs
(SGRBs) has been dramatically increased through the use of ground-based
searches that analyze GBM continuous time tagged event (CTTE) data. Here we
examine the efficiency of a method developed to search CTTE data for
sub-threshold transient events in temporal coincidence with LIGO/Virgo compact
binary coalescence triggers. This targeted search operates by coherently
combining data from all 14 GBM detectors by taking into account the complex
spatial and energy dependent response of each detector. We use the method to
examine a sample of SGRBs that were independently detected by the Burst Alert
Telescope on board the Neil Gehrels Swift Observatory, but which were too
intrinsically weak or viewed with unfavorable instrument geometry to initiate
an on-board trigger of GBM. We find that the search can successfully recover a
majority of the BAT detected sample in the CTTE data. We show that the targeted
search of CTTE data will be crucial in increasing the GBM sensitivity, and
hence the gamma-ray horizon, to weak events such as GRB 170817A. We also
examine the properties of the GBM signal possibly associated with the LIGO
detection of GW150914 and show that it is consistent with the observed
properties of other sub-threshold SGRBs in our sample. We find that the
targeted search is capable of recovering true astrophysical signals as weak as
the signal associated with GW150914 in the untriggered data.Comment: 10 pages, 9 figures, 1 table, submitted to Ap
Swift follow-up observations of candidate gravitational-wave transient events
We present the first multi-wavelength follow-up observations of two candidate
gravitational-wave (GW) transient events recorded by LIGO and Virgo in their
2009-2010 science run. The events were selected with low latency by the network
of GW detectors and their candidate sky locations were observed by the Swift
observatory. Image transient detection was used to analyze the collected
electromagnetic data, which were found to be consistent with background.
Off-line analysis of the GW data alone has also established that the selected
GW events show no evidence of an astrophysical origin; one of them is
consistent with background and the other one was a test, part of a "blind
injection challenge". With this work we demonstrate the feasibility of rapid
follow-ups of GW transients and establish the sensitivity improvement joint
electromagnetic and GW observations could bring. This is a first step toward an
electromagnetic follow-up program in the regime of routine detections with the
advanced GW instruments expected within this decade. In that regime
multi-wavelength observations will play a significant role in completing the
astrophysical identification of GW sources. We present the methods and results
from this first combined analysis and discuss its implications in terms of
sensitivity for the present and future instruments.Comment: Submitted for publication 2012 May 25, accepted 2012 October 25,
published 2012 November 21, in ApJS, 203, 28 (
http://stacks.iop.org/0067-0049/203/28 ); 14 pages, 3 figures, 6 tables;
LIGO-P1100038; Science summary at
http://www.ligo.org/science/Publication-S6LVSwift/index.php ; Public access
area to figures, tables at
https://dcc.ligo.org/cgi-bin/DocDB/ShowDocument?docid=p110003
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