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Theses

Searches for long-duration gravitational wave signals in Advanced Virgo and Advanced LIGO

Abstract : A new astronomy with gravitational waves was born in 2015 with the detection of the first stellar mass black hole merger. Since then, about 50 black hole and neutron star mergers have been observed by the Advanced LIGO and Advanced Virgo detectors during three observation periods. These detections allow to study the populations of compact objects, their mass distribution, and the scenarios of binary system formation. They also allow to study the nature of nuclear matter in extreme environments, the physics of relativistic jets and accretion phenomena, to measure the Hubble constant in an independent way, and to test possible deviations from the theory of general relativity. These observations, now routine, are of major importance and will continue to advance our understanding of the universe during the next observing campaigns. But discovering new astrophysical or cosmological sources of gravitational waves is one of the major objectives of the community and requires additional resources. It is on this subject that this thesis focuses.More precisely, the work summarized in this thesis concerns the search for long duration gravitational wave signals in the Advanced Virgo and Advanced LIGO detectors, i.e. transient signals whose duration is between about 5 and 1000 seconds.The astrophysical processes that can emit this type of gravitational waves are varied, but still poorly modeled. They include potential magneto-hydrodynamic instabilities in newly formed neutron stars, which can make them asymmetric and thus emit gravitational waves, fragmentation processes in accretion disks around black holes, or giant flares that occur in some isolated magnetars, associated with soft gamma-ray bursts. They also include signals from binary systems of rather light black holes in eccentric orbits.Unlike mergers of compact objects, neutron stars and black holes, the waveform of the signal expected here is not sufficiently well modeled to allow the use of optimal signal processing techniques, such as matched filtering. Detection methods therefore rely on algorithms that make few or no assumption about the nature of the signal sought, and are therefore less sensitive.In this thesis, I present a new data analysis pipeline that I have developed to search for unmodeled signals in Advanced Virgo and Advanced LIGO interferometric detectors. This program is based on an already proven method to search signals from a specific point in the sky, and is optimized for searches over the whole sky during an entire observing run. It implements a hierarchical data selection method to reduce the computational time required for analysis, and relies on the correlation of data between multiple detectors to reject artifacts of instrumental and environmental origin.I use this pipeline to search for signals in data from the Advanced Virgo and Advanced LIGO O2 and O3 observing campaigns, and obtain results that do not highlight new sources despite slightly better sensitivity for various signal types. I also show that the computational time was significantly reduced.Finally, I describe the search for gravitational wave counterparts possibly emitted by three giant magnetar flares that seem to constitute a new class of gamma-ray bursts, and show that if such an event were to occur in the galaxy, it would be possible to observe gravitational wave emission if it is at least 1\% as energetic as the electromagnetic emission with the current detectors at their final sensitivity.
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Submitted on : Friday, November 5, 2021 - 9:38:29 AM
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  • HAL Id : tel-03416102, version 1

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Adrian Macquet. Searches for long-duration gravitational wave signals in Advanced Virgo and Advanced LIGO. Astrophysics [astro-ph]. Université Côte d'Azur, 2021. English. ⟨NNT : 2021COAZ4072⟩. ⟨tel-03416102⟩

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