Christopher Allene – Phd’s defense – Sept. 11, 2024

Since 2016 and the first detection of gravitational waves announcement by the Virgo and LIGO collaborations, many other detections produced by compact objects coalescences were made. Most of them come from the coalescence of two black holes but at least one, detected in august 2017, was produced by two coalescing neutron stars. It gave rise to the joint observation of a gamma-ray burst (GRB) and several observations in the electromagnetic domain, which led to the identification of the phenomenon as a kilonova (or macronova). The third observation period of the LIGO-Virgo detectors (‘run’ O3) ended in April 2020. This period is marked by weekly detections of black hole coalescences and by some coalescence candidates including at least a neutron star, which could emit electromagnetic radiation. Multi-messenger astronomy is a key aspect of the advanced detectors scientific program, which should maximize the scientific outcome of the gravitational wave events. Particularly in the case of compact binary coalescences (CBC), the association of a gravitational wave detection with an electromagnetic counterpart is a challenge which has already led to crucial advantages such as unambiguously associating a CBC with a gamma ray burst, providing a precise sky location and an astrophysical context, providing a redshift – thus opening up the possibility of using CBCs as standard sirens to measure the Hubble constant in the local Universe, which has been done with a single event. Since May 2020, the LIGO and Virgo detectors have been stopped to make upgrades before starting a new observation period (‘run’ O4) with better sensitivity in mid-2022, together with the Japanese detector KAGRA. With better sensitivity, the number of sources detected will increase as well as the signal-to-noise ratio of the signals. The LAPP group contributes to a real-time gravitational wave events search program that sends alerts to radio telescopes, optical X and gamma ray telescopes for the most significant candidates in order to search for possible electromagnetic counterparts. Sky maps are simultaneously produced indicating the sky localization probability of the gravitational waves, these maps are used for the pointing of the instruments. In this program, a search for CBC signals was carried out with the MBTA pipeline, developed by the LAPP group in collaboration with the Virgo groups from Urbino (Italy), Strasbourg and Lyon. The aim of the proposed thesis work is to characterize and improve the prospects for detecting electromagnetic counterparts of binary coalescence events. This improvement involves adapting the sky maps produced by MBTA to the specificities of the O4 “run”. This work will then open on – the possible implementation of advanced alerts, or pre-alerts, allowing a gain in latency which is the time between the end of the CBC event and the sending of an alert by MBTA. – the improvement of the program in various aspects such as the extension of the parameter space or the rejection of certain noises always in collaboration with the Virgo groups involved in the program. LAPP’s Virgo group is a major player in the construction, implementation and calibration of Virgo, as well as in the analysis of data from the LIGO-Virgo network. The group has coordinated calibration activities since the construction of Virgo, and, since 2010, has been heavily involved in the real-time alert program for binary system coalescences. The group is also involved in improving stochastic analysis programs.