Strongly lensed supernovae

: a powerful probe of astrophysics and cosmology

Abstract

Strongly lensed supernovae (gLSNe) are a remarkable phenomenon capable of cutting edge cosmological and astrophysical science. The time delays between the multiple lensed images are a direct and independent probe of the Hubble constant (H₀). As a standardisable candle, Type Ia gLSNe promise to measure H₀ with tightly constrained systematics. This is vital to resolve the ongoing tensions between indirect early-Universe and direct late-Universe measurements of H₀, potentially signalling physics beyond the ∧ cold dark matter (∧CDM) model of cosmology. A 1% measurement of H₀ acquired through gLSNe Ia provides a stringent test of ∧CDM. Additionally, gLSNe discovered before the reappearance of the supernova (SN) explosion in the later lensed images provides a unique window into observing the earliest moments of SNe. Such early observations are critical in constraining the progenitor populations of SNe.
This thesis investigates the practicality of using gLSNe to make the above observations. I begin with an introduction to the Hubble constant, supernovae and strong lensing to provide the reader with the context for my research. I then detail the research from Foxley-Marrable et al. (2018), where we discuss the usefulness of gLSNe Ia as a cosmological probe, given the obstacle of stellar microlensing. We show that by considering a sample ∼ 140 gLSNe Ia with asymmetric image configurations, we can measure H0 with systematics constrained at the 0.5% level. I then present research from Foxley-Marrable et al. (2020), where we discuss whether gLSNe can be used to observe the earliest moments of SNe. We predict that Legacy Survey of Space and Time (LSST) will find ∼110 candidate systems per year, with 11.7^+29.8 _-9.3 days between discovery and the SN reappearance. We argue that whilst this will be a challenging undertaking, with significant investment from the astronomical community, deep observations of gLSNe are capable constraining the progenitor populations of SNe. This thesis demonstratively proves the future power of gLSNe when applied to both astrophysics and cosmology.

Date of Award	Dec 2020
Original language	English
Awarding Institution	University of Portsmouth
Supervisor	Thomas Collett (Supervisor), David Bacon (Supervisor) & Robert Nichol (Supervisor)