title: Exploring the calibration of cosmological probes used in gravitational-wave and multi-messenger astronomy
Creators: name: Datrier, Laurence Élise Hélène
Publisher: name: University of Glasgow
Year: 2023

description: The field of gravitational wave astronomy has grown remarkably since the first direct detection of gravitational waves on 14th September 2015. The signal, originating from the merger of two black holes, was detected by the two US-based Advanced LIGO interferometers in Hanford (Washington State) and Livingston (Louisiana). The second observing run of the Advanced LIGO and Virgo detectors marked the first detection of a binary neutron star merger, along with its electromagnetic counterparts. The optical follow-up of the merger led to the first confirmed observations of a kilonova, an electromagnetic counterpart to binary neutron star and neutron star-black hole mergers whose existence was first predicted in 1970s. Following the multimessenger observations of the binary neutron star merger GW170817, constraints were put on the rate of expansion of the Universe using both gravitational wave and electromagnetic data. These measurements could help us understand the current tension between early-Universe and late-Universe measurements of the Hubble constant H0. The use of gravitational wave signals for measuring the rate of expansion of the Universe was proposed by Schutz in 1986. Compact binary coalescences can be used as distance markers, a gravitational wave analogue to standard candles: "Standard Sirens". Measurements of the Hubble constant from standard sirens are independent from previous methods of constraining H0. Bright sirens are gravitational wave signals that are detected coincidentally with electromagnetic signatures. These "bright" gravitational wave sirens are powerful cosmological probes, allowing us to extract information on both the distance and the redshift of the source. It is therefore important to maximise these coincident detections, and to carefully calibrate the data extracted from any standard siren. The work presented in this thesis can be divided into three main topics, all under the umbrella of maximising scientific returns from observations of compact binary coalescences. These three topics are: kilonova parameter estimation, cosmology with gravitational waves, and calibration of advanced gravitational wave detectors. We present work on inferring parameters from kilonova light curves. Ejecta parameters and information about the merging time of the progenitor is extracted from simulated kilonova light curves. We explore the consequence of neglecting some aspects of microphysics on the resulting parameter estimation. We also present new results on the inference of the Hubble constant through the application of a robust test of galaxy catalogue completeness to the current gravitational wave cosmology pipeline. We explore the impact of adopting a robust estimate of the apparent magnitude threshold mthr for the galaxy catalogues used in gravitational wave cosmology on the final inference of the Hubble constant H0 from standard sirens, and compare the results to those obtained when adopting a conservative estimate for mthr. Finally, we present the first results from the prototype of a Newtonian Calibrator at the LIGO Hanford detector. Calibrating the LIGO detectors is crucial to the extraction of the gravitational wave source parameters that are used in cosmology with standard sirens.