202 research outputs found
Robust semicoherent searches for continuous gravitational waves with noise and signal models including hours to days long transients
The vulnerability to single-detector instrumental artifacts in standard
detection methods for long-duration quasimonochromatic gravitational waves from
nonaxisymmetric rotating neutron stars [continuous waves (CWs)] was addressed
in past work [D. Keitel et al., Phys. Rev. D 89, 064023 (2014).] by a Bayesian
approach. An explicit model of persistent single-detector disturbances led to a
generalized detection statistic with improved robustness against such
artifacts. Since many strong outliers in semicoherent searches of LIGO data are
caused by transient disturbances that last only a few hours, we extend the
noise model to cover such limited-duration disturbances, and demonstrate
increased robustness in realistic simulated data. Besides long-duration CWs,
neutron stars could also emit transient signals which, for a limited time, also
follow the CW signal model (tCWs). As a pragmatic alternative to specialized
transient searches, we demonstrate how to make standard semicoherent CW
searches more sensitive to transient signals. Considering tCWs in a single
segment of a semicoherent search, Bayesian model selection yields a new
detection statistic that does not add significant computational cost. On
simulated data, we find that it increases sensitivity towards tCWs, even of
varying durations, while not sacrificing sensitivity to classical CW signals,
and still being robust to transient or persistent single-detector instrumental
artifacts.Comment: 16 pages, 6 figures, REVTeX4.
Line-robust statistics for continuous gravitational waves: safety in the case of unequal detector sensitivities
The multi-detector F-statistic is close to optimal for detecting continuous
gravitational waves (CWs) in Gaussian noise. However, it is susceptible to
false alarms from instrumental artefacts, for example quasi-monochromatic
disturbances ('lines'), which resemble a CW signal more than Gaussian noise. In
a recent paper [Keitel et al 2014, PRD 89 064023], a Bayesian model selection
approach was used to derive line-robust detection statistics for CW signals,
generalising both the F-statistic and the F-statistic consistency veto
technique and yielding improved performance in line-affected data. Here we
investigate a generalisation of the assumptions made in that paper: if a CW
analysis uses data from two or more detectors with very different
sensitivities, the line-robust statistics could be less effective. We
investigate the boundaries within which they are still safe to use, in
comparison with the F-statistic. Tests using synthetic draws show that the
optimally-tuned version of the original line-robust statistic remains safe in
most cases of practical interest. We also explore a simple idea on further
improving the detection power and safety of these statistics, which we however
find to be of limited practical use.Comment: 21 pages, 11 figures, updated to match published versio
The Adaptive Transient Hough method for long-duration gravitational wave transients
This paper describes a new semi-coherent method to search for transient
gravitational waves of intermediate duration (hours to days). In order to
search for newborn isolated neutron stars with their possibly very rapid
spin-down, we model the frequency evolution as a power law. The search uses
short Fourier transforms from the output of ground-based gravitational wave
detectors and applies a weighted Hough transform, also taking into account the
signal's amplitude evolution. We present the technical details for implementing
the algorithm, its statistical properties, and a sensitivity estimate. A first
example application of this method was in the search for GW170817 post-merger
signals, and we verify the estimated sensitivity with simulated signals for
this case.Comment: 13 pages, 14 figure
Galactic Double Neutron Star total masses and Gaussian mixture model selection
Huang et al. [arXiv:1804.03101] have analysed the population of 15 known
galactic Double Neutron Stars (DNSs) regarding the total masses of these
systems. They suggest the existence of two sub-populations, and report
likelihood-based preference for a two-component Gaussian mixture model over a
single Gaussian distribution. This note offers a cautionary perspective on
model selection for this data set: Especially for such a small sample size, a
pure likelihood ratio test can encourage overfitting. This can be avoided by
penalising models with a higher number of free parameters. Re-examining the DNS
total mass data set within the class of Gaussian mixture models, this can be
achieved through several simple and well-established statistical tests,
including information criteria (AICc, BIC), cross-validation, Bayesian evidence
ratios and a penalised EM-test. While this re-analysis confirms the basic
finding that a two-component mixture is consistent with the data, the model
selection criteria consistently indicate that there is no robust preference for
it over a single-component fit. Additional DNS discoveries will be needed to
settle the question of sub-populations.Comment: 9 pages and 10 figures including appendices, updated version as
accepted by MNRA
An F-statistic based multi-detector veto for detector artifacts in continuous-wave gravitational wave data
Continuous gravitational waves (CW) are expected from spinning neutron stars
with non-axisymmetric deformations. A network of interferometric detectors
(LIGO, Virgo and GEO600) is looking for these signals. They are predicted to be
very weak and retrievable only by integration over long observation times. One
of the standard methods of CW data analysis is the multi-detector F-statistic.
In a typical search, the F-statistic is computed over a range in frequency,
spin-down and sky position, and the candidates with highest F values are kept
for further analysis. However, this detection statistic is susceptible to a
class of noise artifacts, strong monochromatic lines in a single detector. By
assuming an extended noise model - standard Gaussian noise plus single-detector
lines - we can use a Bayesian odds ratio to derive a generalized detection
statistic, the line veto (LV-) statistic. In the absence of lines, it behaves
similarly to the F-statistic, but it is more robust against line artifacts. In
the past, ad-hoc post-processing vetoes have been implemented in searches to
remove these artifacts. Here we provide a systematic framework to develop and
benchmark this class of vetoes. We present our results from testing this
LV-statistic on simulated data.Comment: 2 pages, 1 figure, to be published in Proceedings of Statistical
Challenges in Modern Astronomy V, Springer 201
Faster search for long gravitational-wave transients: GPU implementation of the transient F-statistic
The F-statistic is an established method to search for continuous
gravitational waves from spinning neutron stars. Prix et al. (2011) introduced
a variant for transient quasi-monochromatic signals. Possible astrophysical
scenarios for such transients include glitching pulsars, newborn neutron stars
and accreting systems. Here we present a new implementation of the transient
F-statistic, using pyCUDA to leverage the power of modern graphics processing
units (GPUs). The obtained speedup allows efficient searches over much wider
parameter spaces, especially when using more realistic transient signal models
including time-varying (e.g. exponentially decaying) amplitudes. Hence, it can
enable comprehensive coverage of glitches in known nearby pulsars, improve the
follow-up of outliers from continuous-wave searches, and might be an important
ingredient for future blind all-sky searches for unknown neutron stars.Comment: 13 pages, 3 figures; v2: updated reference to 1710.02327 and its
erratu
Waveform systematics in identifying gravitationally lensed gravitational waves: Posterior overlap method
Gravitational lensing has been extensively observed for electromagnetic
signals, but not yet for gravitational waves (GWs). Detecting lensed GWs will
have many astrophysical and cosmological applications, and becomes more
feasible as the sensitivity of the LIGO-Virgo-KAGRA detectors improves. One of
the missing ingredients to robustly identify lensed GWs is to ensure that the
statistical tests used are robust under the choice of underlying waveform
models. We present the first systematic study of possible waveform systematics
in identifying candidates for strongly lensed GW event pairs, focusing on the
posterior overlap method. To this end, we compare Bayes factors from all
posteriors using different waveforms included in GWTC data releases from the
first three observing runs (O1-O3). We find that waveform choice yields a wide
spread of Bayes factors in some cases. However, it is likely that no event
pairs from O1 to O3 were missed due to waveform choice. We also perform
parameter estimation with additional waveforms for interesting cases, to
understand the observed differences. We also briefly explore if computing the
overlap from different runs for the same event can be a useful metric for
waveform systematics or sampler issues, independent of the lensing scenario.Comment: 29 pages, 5 figures, comments welcom
Matched-filter study and energy budget suggest no detectable gravitational-wave 'extended emission' from GW170817
Van Putten & Della Valle (2018) have reported a possible detection of
gravitational-wave 'extended emission' from a neutron star remnant of GW170817.
Starting from the time-frequency evolution and total emitted energy of their
reported candidate, we show that such an emission is not compatible with the
current understanding of neutron stars. We explore the additional required
physical assumptions to make a full waveform model, for example, taking the
optimistic emission from a spining-down neutron star with fixed quadrupolar
deformation, and study whether even an ideal single-template matched-filter
analysis could detect an ideal, fully phase-coherent signal. We find that even
in the most optimistic case an increase in energy and extreme parameters would
be required for a confident detection with LIGO sensitivity as of 2018-08-17.
The argument also holds for other waveform models following a similar
time-frequency track and overall energy budget. Single-template matched
filtering on the LIGO data around GW170817, and on data with added simulated
signals, verifies the expected sensitivity scaling and the overall statistical
expectation.Comment: 9 pages, 6 figures, updated version as accepted by MNRA
Convolutional neural network search for long-duration transient gravitational waves from glitching pulsars
Machine learning can be a powerful tool to discover new signal types in
astronomical data. We here apply it to search for long-duration transient
gravitational waves triggered by pulsar glitches, which could yield physical
insight into the mostly unknown depths of the pulsar. Current methods to search
for such signals rely on matched filtering and a brute-force grid search over
possible signal durations, which is sensitive but can become very
computationally expensive. We develop a method to search for post-glitch
signals on combining matched filtering with convolutional neural networks,
which reaches similar sensitivities to the standard method at false-alarm
probabilities relevant for practical searches, while being significantly
faster. We specialize to the Vela glitch during the LIGO-Virgo O2 run, and set
upper limits on the gravitational-wave strain amplitude from the data of the
two LIGO detectors for both constant-amplitude and exponentially decaying
signals.Comment: 19 pages, 9 figures. Comments welcom
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