Targeted searches for continuous gravitational waves

authored by: Anjana Ashok
supervised by: Maria Alessandra Papa
Abstract: Gravitational waves are a consequence of Albert Einstein’s General theory of relativity, which he put forward in 1916. One hundred years later, in 2015, a gravitational wave signal from two merging black holes was detected by the Advanced LIGO detectors. Now, the Advanced LIGO detectors have recorded about a hundred such signals from the merging of compact objects in binary systems. Rotating neutron stars with a non-axisymmetric distribution of their mass present a perfect candidate for emitting gravitational waves continuously. Such continuous gravitational waves are several orders of magnitude weaker than those emitted by merging binary systems. Not surprisingly, these continuous gravitational wave signals have not yet been detected in the Advanced LIGO data. Efforts to make a detection of such a signal are going on. This thesis presents such a search for continuous gravitational waves. Pulsars are neutron stars from which electromagnetic emissions have been observed, most commonly in the radio wavelength. These observations provide useful information about the neutron star, including its location in the sky and spin parameters. With this knowledge, we search for the continuous gravitational wave from that specific neutron star – thus targeting a source. Such targeted searches probe a small region of the signal parameter space and hence can afford a fully coherent search in data from all observations of the detectors. This makes targeted searches the most sensitive search strategy. In this thesis, we present two different methods to search for continuous gravitational wave signals from pulsars. Using these methods, we target newly discovered, fast-spinning pulsars, a majority of them in binary systems. These pulsars have been targeted for continuous gravitational wave emission for the first time in this work. We do not detect a continuous gravitational wave signal from any of the targets. The non-detection of a signal can be translated into constraints on the mass distortions of the pulsar, parameterized by its ‘ellipticity’. Our constraints on the ellipticities of these pulsars, using data from all the observation runs of Advanced LIGO detectors, are some of the lowest and lie in the regime of astrophysically interesting values for the parameter.
Organisation(s): Institute of Gravitation Physics
QUEST-Leibniz Research School
Type: Doctoral thesis
No. of pages: 221
Publication date: 2023
Publication status: Published
Electronic version(s): https://doi.org/10.15488/14733 (Access: Open)
: Details in the research portal "Research@Leibniz University"

BibTeX

@phdthesis{93dbd1823b4543c3807b2c314eafc802,
title = "Targeted searches for continuous gravitational waves",
abstract = "Gravitational waves are a consequence of Albert Einstein{\textquoteright}s General theory of relativity, which he put forward in 1916. One hundred years later, in 2015, a gravitational wave signal from two merging black holes was detected by the Advanced LIGO detectors. Now, the Advanced LIGO detectors have recorded about a hundred such signals from the merging of compact objects in binary systems. Rotating neutron stars with a non-axisymmetric distribution of their mass present a perfect candidate for emitting gravitational waves continuously. Such continuous gravitational waves are several orders of magnitude weaker than those emitted by merging binary systems. Not surprisingly, these continuous gravitational wave signals have not yet been detected in the Advanced LIGO data. Efforts to make a detection of such a signal are going on. This thesis presents such a search for continuous gravitational waves. Pulsars are neutron stars from which electromagnetic emissions have been observed, most commonly in the radio wavelength. These observations provide useful information about the neutron star, including its location in the sky and spin parameters. With this knowledge, we search for the continuous gravitational wave from that specific neutron star – thus targeting a source. Such targeted searches probe a small region of the signal parameter space and hence can afford a fully coherent search in data from all observations of the detectors. This makes targeted searches the most sensitive search strategy. In this thesis, we present two different methods to search for continuous gravitational wave signals from pulsars. Using these methods, we target newly discovered, fast-spinning pulsars, a majority of them in binary systems. These pulsars have been targeted for continuous gravitational wave emission for the first time in this work. We do not detect a continuous gravitational wave signal from any of the targets. The non-detection of a signal can be translated into constraints on the mass distortions of the pulsar, parameterized by its {\textquoteleft}ellipticity{\textquoteright}. Our constraints on the ellipticities of these pulsars, using data from all the observation runs of Advanced LIGO detectors, are some of the lowest and lie in the regime of astrophysically interesting values for the parameter.",
author = "Anjana Ashok",
year = "2023",
doi = "10.15488/14733",
language = "English",
publisher = "Leibniz Universit{\"a}t Hannover",
school = "Leibniz University Hannover",
}