17 research outputs found
Improved detection statistics for non Gaussian gravitational wave stochastic backgrounds
In a recent paper we described a novel approach to the detection and
parameter estimation of a non-Gaussian stochastic background of gravitational
waves. In this work we propose an improved version of the detection procedure,
preserving robustness against imperfect noise knowledge at no cost of detection
performance: in the previous approach, the solution proposed to ensure
robustness reduced the performances of the detection statistics, which in some
cases (namely, mild non-Gaussianity) could be outperformed by Gaussian ones
established in literature. We show, through a simple toy model, that the new
detection statistic performs better than the previous one (and than the
Gaussian statistic) everywhere in the parameter space. It approaches the
optimal Neyman-Pearson statistics monotonically with increasing non-Gaussianity
and/or number of detectors. In this study we discuss in detail its efficiency.
This is a second, important step towards the implementation of a
nearly--optimal detection procedure for a realistic non-Gaussian stochastic
background. We discuss the relevance of results obtained in the context of the
toy model used, and their importance for understanding a more realistic
scenario.Comment: 12 pages, 5 figures (published on 23 June 2023
Detecting non-Gaussian gravitational wave backgrounds: a unified framework
We describe a novel approach to the detection and parameter estimation of a
non\textendash Gaussian stochastic background of gravitational waves. The
method is based on the determination of relevant statistical parameters using
importance sampling. We show that it is possible to improve the Gaussian
detection statistics, by simulating realizations of the expected signal for a
given model. While computationally expensive, our method improves the detection
performance, leveraging the prior knowledge on the expected signal, and can be
used in a natural way to extract physical information about the background. We
present the basic principles of our approach, characterize the detection
statistic performances in a simplified context and discuss possible
applications to the detection of some astrophysical foregrounds. We argue that
the proposed approach, complementarily to the ones available in literature
might be used to detect suitable astrophysical foregrounds by currently
operating and future gravitational wave detectors.Comment: 12 Pages, 4 Figures, Supplemental material (published on 24 March
2023
Upper limits on persistent gravitational waves using folded data and the full covariance matrix from Advanced LIGOs first two observing runs
The stochastic gravitational wave background (SGWB) created by astrophysical
sources in the nearby universe is likely to be anisotropic. Upper limits on
SGWB anisotropy have been produced for all major data taking runs by the
ground-based laser interferometric detectors. However, due to the challenges
involved in numerically inverting the pixel-to-pixel noise covariance matrix,
which is necessary for setting upper limits, the searches accounted for angular
correlations in the map by using the spherical harmonic basis, where
regularization was relatively easier. This approach is better suited though for
extended sources.Moreover, the upper limit maps produced in the two different
bases are seemingly different. While the upper limits may be consistent within
statistical errors, it was important to check whether the results would remain
consistent if the full noise covariance matrix was used in the pixel basis.
Here, we use the full pixel-to-pixel Fisher information matrix to create upper
limit maps of SGWB anisotropy. We first perform an unmodeled search for
persistent, directional gravitational wave sources using folded data from the
first (O1) and second (O2) observing runs of Advanced LIGO and show that the
results are consistent with the upper limits published by the LIGO-Virgo
Collaboration (LVC). We then explore various ways to account for the
pixel-to-pixel Fisher information matrix using singular value decomposition and
Bayesian regularization schemes. We also account for the bias arising from
regularization in the likelihood. We do not find evidence for any SGWB signal
in the data, consistent with the LVC results and, though the upper limits
differ significantly. Through an injection study we show that they are all
valid upper limits, that is, the upper limit in a pixel is less than the
injected signal strength in less than of the pixels.Comment: 17 pages, 7 figure