Paul Lagabbe – Phd’s defense – Oct. 22, 2023
Towards an accurate Virgo gravitational wave strain reconstruction for real-time multi-messenger astronomy
In August 2017, the first LIGO-Virgo joint observation of gravitational waves coming from a neutron star inspiral and a gamma ray burst, followed by an optical signal, opened a new chapter of astronomy. Besides confirming binary neutron star mergers as progenitors of short gamma ray bursts, new kinds of measurements have been made, from general relativity tests to independent determination of the Hubble constant within a precision of 15%. The third LIGO-Virgo observation run has started in April 2019 and was completed in April 2020. This run was marked by weekly detections of binary black hole coalescences and by few candidates for coalescences including at least one neutron star. Within minutes, such detection generates public alerts to trigger multi-messenger observations of the sources. From May 2020, the LIGO and Virgo detectors will be stopped to upgrade the detectors and will start a new observation run with better sensitivities by the end 2021, jointly with the Japanese Kagra detector. Increasing their sensitivity will further increase the number of observed sources and their signal-to-noise ratio. For generating fast and precise alerts for multi-messenger astronomy and extract most of the physics from the detected events, it is of main importance to reduce the latency and to improve the precision of both the calibration and analysis. For every Observing Run, an important detector calibration activity is needed to reconstruct the gravitational wave signal from various signals measured within the interferometer.
Having more and more detections in the coming years, the precision of the detector calibration and the precision of the gravitational wave signal reconstruction will need to be better controlled. In addition, the inter-calibration of the detectors LIGO, Virgo and Kagra is of main importance to properly estimate the parameters of the sources detected by the worldwide network. The electromagnetic follow-up program for gravitational waves relies on real time analysis of LIGO, Virgo (and Kagra soon) data followed by alerts that are public. Its effectiveness is critical to observe the weak and transient electromagnetic counterparts, to then extract in particular cosmological, astrophysical and fundamental physics parameters. The LAPP Virgo group is a major actor in the construction, operation and calibration of the Virgo detector, and in data analysis of the LIGO-Virgo network. It has been coordinating the calibration activities since the construction of Virgo and, since 2010, the group has been involved in the low latency alert program for binary coalescing systems. This search, on the LIGO and Virgo data, uses the MBTA analysis software developed at LAPP. A PhD thesis with key activities on reducing the latency and improving the precision of the calibration and data analysis is proposed. Trips to the US are to be considered, in particular in the context of the LIGO-Virgo cross-calibration activities.