Coherent network analysis is addressing the problem of detection and reconstruction of gravitational waves (GW) with networks of detectors. It has been extensively studied in the literature in application to detection of bursts signals, which may be produced by numerous gravitational wave sources in the Universe. In coherent methods, a statistic is built up as a coherent sum over detector responses. In general, it is expected to be more optimal (better sensitivity at the same false alarm rate) than the detection statistics of the individual detectors that make up the network. Also coherent methods provide estimators for the GW waveforms and the source coordinates in the sky. The method we present (called coherent WaveBurst) is significantly different from the traditional burst detection methods. Unlike coincident methods, which first identify events in individual detectors by using an excess power statistic and than require coincidence between detectors, the coherent WaveBurst method combines all data streams into one coherent statistic constructed in the framework of the constrained maximum likelihood analysis. Such an approach has significant advantages over the coincident methods. First, the sensitivity of the method is not limited by the least sensitive detector in the network. In the coherent WaveBurst method the detection is based on the maximum likelihood ratio statistic which represents the total signal-to-noise ratio of the GW signal detected in the network. Second, other coherent statistics, such as the null stream and the network correlation coefficient can be constructed to distinguish genuine GW signals from the environmental and instrumental artifacts. Finally, the source coordinates of the GW waveforms can be reconstructed.

  • Extracted from: S. Klimenko, I. Yakushin , A. Mercer, G. Mitselmakher , Coherent method for detection of gravitational wave bursts, Class. Quantum Grav. 25, 114029 (2008): link to CQG, link to arXiv

Advanced LIGO detectors [1] has started their operation at unprecedented sensitivity targeting first detection of gravitational waves from astrophysical sources. A more robust detection of gravitational waves is anticipated in the next few years as the advanced LIGO reaches its designed sensitivity and the other advanced detectors Virgo [2] Kagra [3] and LIGO-India [4] come online. Numerous GW signals, expected to be observed by the advanced detectors ( 40 binary neutron star and possible black hole mergers per year [5] will begin our exploration of the gravitational-wave sky and start the era of the gravitational wave astronomy. The advanced detectors target detection of GW transients for a wide range of promising astrophysical sources including: various types of gamma-ray bursts, core-collapse supernovae, soft-gamma repeaters, cosmic strings, late inspiral and mergers of compact binaries, ring-downs of perturbed neutron stars or black holes, and as-yet-unknown systems. Most of these sources are difficult to model, due to their complicated dynamics and because the equation of state of matter at neutron star densities is not known. Therefore, the search algorithms have been developed for detection of GW transients, or bursts of GW radiation in the detector bandwidth, with no or little assumptions on the source models. There are two different ways the GW searches are conducted: in real time and searches on the archived data. The objective of the real time burst search is the identification and reconstruction of significant event candidates with low latency (within few minutes). The reconstructed sky location can be promptly shared with the partner telescopes, which search for a coincident electromagnetic (EM) counterpart [10] [11] A prominent source for such join observation is a merger of compact binary objects where one of the companions (or both) is a neutron star. Such mergers may produce several EM signals: gamma-ray busts (GRB), GRB afterglow, kilonova, etc, which will fade away with the time scales ranging from seconds to days [12] A small fraction of such mergers (when the GRB beam is pointing at us) can be independently detected by the gamma-ray telescopes and associated with a GW signal by the time of the event. However, most of the compact binary mergers require a prompt sky localization with the GW detectors and follow-up EM searches for possible afterglow. Similar observations can be performed for the galactic events such as supernovae or soft-gamma-repeaters, which may produce both the EM and neutrino counterparts. On contrary, the objective of the archived burst analysis is to establish a significance of observed events and identify their progenitors. Such analysis requires detail background studies and accurate reconstruction of the source parameters, which may not be readily available with low latency. Both types of searches and the sky localization studies have been performed with the baseline burst algorithm coherent WaveBurst (cWB) [6] used in the analysis of data form the initial instruments. In this paper we describe the improvements of the cWB algorithm, which is currently used both for the real time burst search and several archived searches with the networks of advanced detectors. This second generation cWB algorithm includes several novelties. The time-frequency analysis has been updated with a novel time frequency transform [20] which improved the waveform reconstruction. It also significantly improved the computational performance of the algorithm, enabling a robust low latency operation. The data conditioning (whitening, removal of the spectral artifacts, etc) has been enhanced with the data regression algorithms [21] Fast reconstruction of the chirp mass [22] has been introduced to enable rapid identification of the compact binary coalescence (CBC) sources. The extensive sky localization studies have been performed [23]

  • Extracted from: S. Klimenko, G. Vedovato, M. Drago, F. Salemi, V. Tiwari, G.A. Prodi, C. Lazzaro, K. Ackley, S. Tiwari, C.F. Da Silva, and G. Mitselmakher, Method for detection and reconstruction of gravitational wave transients with networks of advanced detectors, Phys. Rev. D 93, 042004 (2016): link to PRD, link to arXiv


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