The 28th July of 2020 Josep Blai Covas Vidal present his thesis: Searching for continuous gravitational waves with advanced LIGO
The first direct detection of gravitational waves (GWs) on September 142015 marked the beginning of gravitational-wave astronomy. All of the GWs that havebeen detected until now came from compact binary coalescences, a type of signal thatis detectable during seconds or a few minutes. A completely different type of gravitational waves are continuous gravitational waves (CWs), which are long-lasting waves mainly produced by asymmetric rotating neutron stars, either isolated or inbinary systems. Although many searches for CWs have been done, none of them has reported a detection. Even though CWs can be tracked during much longer times than compact binary coalescences, the amplitude of these gravitational waves is expected to be many orders of magnitude smaller: the amplitude of the detected GWs is around 10-21, whereas CW searches are constraining this amplitude to be less than 10-26 for some pulsars, which clearly underlines the challenge of detecting CWs. CW searches can be divided between searches for GWs from known pulsars and searches for GWs from unknown neutron stars. Unlike searches for GWs from pulsars (whose locations, gravitational wave emission frequencies, and spin-down rates are well known), searches for electromagnetically quiet sources require algorithms that look at vastly larger parameter spaces, because the data has to be correlated with theoretical waveforms that depend on these unknown parameters, which have to be included to take into account the different modulations such as the Doppler modulation produced by Earth’s rotation and orbit around the sun. Unfortunately, there is not enough computing power available to search such a large and nearly continuous parameter space in sky position, frequency, and spin-down rate. For this reason, developing non-optimal algorithms that can deal with this huge parameter
space is an important task within the data analysis community. This thesis is separated in two different parts. The first part is made up of three chapters that give introductions to different topics that are needed to understand CW searches: how gravitational waves are generated and propagated, what neutron stars are and how they can generate gravitational waves, and what statistical methods have to be used in order to detect a CW signal and estimate its parameters. The second partis made up of four chapters that summarize original results that have been published in high-impact journals.
Author: Josep Blai Covas Vidal
Title: Searching for continuous gravitational waves with advanced LIGO
Director: Dr. Alicia Sintes
Date: 28 July 2020