11 research outputs found
Bayesian Inference Analysis of Unmodelled Gravitational-Wave Transients
We report the results of an in-depth analysis of the parameter estimation
capabilities of BayesWave, an algorithm for the reconstruction of
gravitational-wave signals without reference to a specific signal model. Using
binary black hole signals, we compare BayesWave's performance to the
theoretical best achievable performance in three key areas: sky localisation
accuracy, signal/noise discrimination, and waveform reconstruction accuracy.
BayesWave is most effective for signals that have very compact time-frequency
representations. For binaries, where the signal time-frequency volume decreases
with mass, we find that BayesWave's performance reaches or approaches
theoretical optimal limits for system masses above approximately 50 M_sun. For
such systems BayesWave is able to localise the source on the sky as well as
templated Bayesian analyses that rely on a precise signal model, and it is
better than timing-only triangulation in all cases. We also show that the
discrimination of signals against glitches and noise closely follow analytical
predictions, and that only a small fraction of signals are discarded as
glitches at a false alarm rate of 1/100 y. Finally, the match between
BayesWave- reconstructed signals and injected signals is broadly consistent
with first-principles estimates of the maximum possible accuracy, peaking at
about 0.95 for high mass systems and decreasing for lower-mass systems. These
results demonstrate the potential of unmodelled signal reconstruction
techniques for gravitational-wave astronomy.Comment: 10 pages, 7 figure
Detection, reconstruction and interpretation of unmodelled gravitational-wave transients
In this thesis we aim to answer a number of key questions related to unmodelled gravitational-wave (GW) transients, namely: (1) how can we detect an unmodelled GW transient (‘burst’); (2) how well can we reconstruct GW burst parameters; (3) how can we infer the structure of an unmodelled GW source based on the observed signal.
Chapter 1 introduces GW astronomy: how gravitational waves are produced, what are the main categories of GW sources, and how GW detectors work. We end the chapter with a summary of the Advanced LIGO (Laser Interferometer Gravitational-wave Observatory) and Virgo observing runs.
In Chapter 2 we describe the most promising sources of unmodelled GW transients such as gamma-ray bursts (GRBs), supernovae (SNe), isolated neutron stars and fast radio bursts (FRBs). We focus on the short GRB–compact binary coalescence (CBC) and long GRB–supernova progenitor models.
In the following chapter (Ch. 3) we present X-Pipeline, a coherent search pipeline for GW bursts. We define a theoretical framework necessary to perform a coherent analysis with X-Pipeline, and describe how X-Pipeline can be used for searches for GWs associated with GRBs. In the second part of the chapter we report results of such analyses for the LIGO–Virgo Observing runs 2 and 3a.
Chapter 4 presents a study that answers the question no. 2, i.e. how well can we reconstruct GW burst parameters, especially the waveform h(t). We perform an injection study with BayesWave, a Bayesian parameter estimation algorithm, using binary black hole (BBH) signals in LIGO–Virgo data. We assess BayesWave performance against the first-principle estimates in three key areas: sky localisation accuracy, signal/noise discrimination, and waveform reconstruction accuracy.
Finally, Chapter 5 introduces a novel technique to reconstruct a source mass density perturbation from the GW signal h(t). We start by deriving the algorithm and testing it with multiple sample sources. We describe in more detail why the algorithm is unable to reconstruct the radial evolution of a BBH merger, and provide a Bayesian framework that could solve this issue by including additional constraints. We end the chapter by discussing the method’s limitations, possible solutions and future development work
Antiglitch: a Quasi-physical Model for Removing Short Glitches from LIGO and Virgo Data
Gravitational-wave observatories become more sensitive with each observing
run, increasing the number of detected gravitational-wave signals. A limiting
factor in identifying these signals is the presence of transient non-Gaussian
noise, which generates glitches that can mimic gravitational wave signals. Our
work provides a quasi-physical model waveform for the four most common types of
short transient glitches, which are particularly problematic in the search for
high-mass black hole binaries. Our model has only a few, physically
interpretable parameters: central frequency, bandwidth, phase, amplitude and
time. We demonstrate the accuracy of this model by fitting and removing a large
sample of glitches from a month of LIGO and Virgo data from the O3 observing
run. We can effectively remove three of the four types of short transients. We
finally map the ability of these glitches to mimic binary black hole signals.Comment: 13 pages, 14 Figures, Submitted to Phys.Rev.
Revisiting the evidence for precession in GW200129 with machine learning noise mitigation
GW200129 is claimed to be the first-ever observation of the spin-disk orbital precession detected with gravitational waves (GWs) from an individual binary system. However, this claim warrants a cautious evaluation because the GW event coincided with a broadband noise disturbance in LIGO Livingston caused by the 45 MHz electro-optic modulator system. In this paper, we present a state-of-the-art neural network that is able to model and mitigate the broadband noise from the LIGO Livingston interferometer. We also demonstrate that our neural network mitigates the noise better than the algorithm used by the LIGO-Virgo-KAGRA collaboration. Finally, we re-analyse GW200129 with the improved data quality and show that the evidence for precession is still observed
Point absorbers in Advanced LIGO
Small, highly absorbing points are randomly present on the surfaces of the
main interferometer optics in Advanced LIGO. The resulting nano-meter scale
thermo-elastic deformations and substrate lenses from these micron-scale
absorbers significantly reduces the sensitivity of the interferometer directly
though a reduction in the power-recycling gain and indirect interactions with
the feedback control system. We review the expected surface deformation from
point absorbers and provide a pedagogical description of the impact on power
build-up in second generation gravitational wave detectors (dual-recycled
Fabry-Perot Michelson interferometers). This analysis predicts that the
power-dependent reduction in interferometer performance will significantly
degrade maximum stored power by up to 50% and hence, limit GW sensitivity, but
suggests system wide corrections that can be implemented in current and future
GW detectors. This is particularly pressing given that future GW detectors call
for an order of magnitude more stored power than currently used in Advanced
LIGO in Observing Run 3. We briefly review strategies to mitigate the effects
of point absorbers in current and future GW wave detectors to maximize the
success of these enterprises.Comment: 49 pages, 16 figures. -V2: typographical errors in equations B9 and
B10 were corrected (stray exponent of "h" was removed). Caption of Figure 9
was corrected to indicate that 40mW was used for absorption in the model, not
10mW as incorrectly indicated in V
First narrow-band search for continuous gravitational waves from known pulsars in advanced detector data
International audienceSpinning neutron stars asymmetric with respect to their rotation axis are potential sources of continuous gravitational waves for ground-based interferometric detectors. In the case of known pulsars a fully coherent search, based on matched filtering, which uses the position and rotational parameters obtained from electromagnetic observations, can be carried out. Matched filtering maximizes the signal-to-noise (SNR) ratio, but a large sensitivity loss is expected in case of even a very small mismatch between the assumed and the true signal parameters. For this reason, narrow-band analysis methods have been developed, allowing a fully coherent search for gravitational waves from known pulsars over a fraction of a hertz and several spin-down values. In this paper we describe a narrow-band search of 11 pulsars using data from Advanced LIGO’s first observing run. Although we have found several initial outliers, further studies show no significant evidence for the presence of a gravitational wave signal. Finally, we have placed upper limits on the signal strain amplitude lower than the spin-down limit for 5 of the 11 targets over the bands searched; in the case of J1813-1749 the spin-down limit has been beaten for the first time. For an additional 3 targets, the median upper limit across the search bands is below the spin-down limit. This is the most sensitive narrow-band search for continuous gravitational waves carried out so far
Model comparison from LIGO–Virgo data on GW170817’s binary components and consequences for the merger remnant
International audienceGW170817 is the very first observation of gravitational waves originating from the coalescence of two compact objects in the mass range of neutron stars, accompanied by electromagnetic counterparts, and offers an opportunity to directly probe the internal structure of neutron stars. We perform Bayesian model selection on a wide range of theoretical predictions for the neutron star equation of state. For the binary neutron star hypothesis, we find that we cannot rule out the majority of theoretical models considered. In addition, the gravitational-wave data alone does not rule out the possibility that one or both objects were low-mass black holes. We discuss the possible outcomes in the case of a binary neutron star merger, finding that all scenarios from prompt collapse to long-lived or even stable remnants are possible. For long-lived remnants, we place an upper limit of 1.9 kHz on the rotation rate. If a black hole was formed any time after merger and the coalescing stars were slowly rotating, then the maximum baryonic mass of non-rotating neutron stars is at most , and three equations of state considered here can be ruled out. We obtain a tighter limit of for the case that the merger results in a hypermassive neutron star
Open data from the first and second observing runs of Advanced LIGO and Advanced Virgo
Advanced LIGO and Advanced Virgo are monitoring the sky and collecting gravitational-wave strain data with sufficient sensitivity to detect signals routinely. In this paper we describe the data recorded by these instruments during their first and second observing runs. The main data products are gravitational-wave strain time series sampled at 16384 Hz. The datasets that include this strain measurement can be freely accessed through the Gravitational Wave Open Science Center at http://gw-openscience.org, together with data-quality information essential for the analysis of LIGO and Virgo data, documentation, tutorials, and supporting software