STRONGLY LENSED SUPERNOVAE: A POWERFUL PROBE OFASTROPHYSICSANDCOSMOLOGY max foxley-marrable A thesis submitted in partial fulfilment of the requirements for the award of the degree of Doctor of Philosophy Institute of Cosmology and Gravitation Faculty of Technology University of Portsmouth December 2020 Max Foxley-Marrable: Strongly Lensed Supernovae: A Powerful Probe of Astrophysics and Cosmology. A thesis submitted in partial fulfilment of the requirements for the award of the degree of Doctor of Philosophy, © December 2020 supervisors: Dr. Thomas Collett Prof. Bob Nichol Prof. David Bacon “The best scientific minds of the system were staring at the data with their jaws slack, and the reason no one was panicking yet was that no one could agree on what they should panic about.” — James S.A. Corey, Caliban’s War ABSTRACT Strongly lensed supernovae (gLSNe) are a remarkable phenomenon capable of cutting- edge cosmological and astrophysical science. The time delays between the multi- ple 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 con- strained 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 Λ cold dark matter (ΛCDM) model of cosmology. A 1% measure- ment of H0 acquired through gLSNe Ia provides a stringent test of ΛCDM. 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 observa- tions. 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 re- search 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 +29.8 Time (LSST) will find ∼ 110 candidate systems per year, with 11.7-9.3 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 ob- servations of gLSNe are capable constraining the progenitor populations of SNe. This thesis demonstratively proves the future power of gLSNe when applied to both astro- physics and cosmology. iv PUBLICATIONS Chapters 4 and 5 have appeared previously in the following publications: Foxley-Marrable, Max, Thomas E. Collett, Chris Frohmaier, Daniel A. Goldstein, Daniel Kasen, Elizabeth Swann, and David Bacon (May 2020). “Observing the earliest moments of supernovae using strong gravitational lenses.” In: MNRAS. doi: 10.1093/mnras/staa1289. arXiv: 2003.14340 [astro-ph.HE]. Foxley-Marrable, Max, Thomas E. Collett, Georgios Vernardos, Daniel A. Goldstein, and David Bacon (Aug. 2018). “The impact of microlensing on the standardiza- tion of strongly lensed Type Ia supernovae.” In: Monthly Notices of the RAS 478.4, pp. 5081–5090. doi: 10.1093/mnras/sty1346. arXiv: 1802.07738 [astro-ph.CO]. v ACKNOWLEDGEMENTS I am forever indebted to my first supervisor Thomas Collett. Your guidance and ex- pertise has allowed me to achieve what I frequently believed to be an insurmountable task. My frequent struggles with mental health and self-confidence have not made this process an easy road, however you remained patient and supportive throughout. Considering I was your first student, the way you have adapted to provide a level of supervision expected from those beyond your years of experience, is nothing short of commendable. I am so proud of what we have achieved over the years. I also want to extend my heartfelt thanks to David Bacon. You have been a constant source of emotional guidance and have always made time out of your busy schedule to aid me in my times of need. Even during moments of utter despair, meetings with you always left me hopeful and optimistic about the future. I want to express sincere gratitude towards my collaborators: Daniel Goldstein, Chris Frohmaier, Georgios Vernardos, Daniel Kasen and Elizabeth Swann, whose key contributions and thoughtful insights made the published works presented a reality. I also want to thank my colleagues at the Institute of Cosmology and Gravitation and all of my friends, both in and outside of academia. I want to extend a special mention to my UK Tech-Fest and ArcTanGent family. Getting to hang out with you guys every year, nerding out to incredible music and laughing until I can’t breathe - I truly feel myself and at home. To my loved ones, in particular my Mum and Dad, whose support over the past ∼ 27 years have enabled me to pursue my passion and without I would not be here today... quite literally. To my partner Alexandra, I cannot even begin to express how much your love and words of encouragement enabled me to keep on going. Even during my darkest moments you remained a rock and kept me grounded. You have enriched my life beyond words and I look forward to the day when there isn’t an ocean separating us. I’m extremely lucky to be with someone as wonderful as you. Simply put, without all your support, this thesis would not exist. I dedicate this work to all of you. vi CONTENTS i introduction1 1 the hubble constant2 1.1 A Brief History . 2 1.2 Tensions in the Hubble Constant . 3 1.3 Theory . 7 1.3.1 Measuring Distances . 9 1.4 One-Step Distance Methods . 10 1.4.1 Megamasers . 10 1.4.2 Strong Gravitational Lensing . 11 1.4.3 Gravitational Waves . 15 1.5 The Cosmic Distance Ladder . 17 1.5.1 Overview . 17 1.5.2 Stellar Parallax . 18 1.5.3 Type Ia Supernovae . 19 1.5.4 Distance Ladder Calibrators . 20 1.5.5 Inverse Distance Ladder . 23 1.6 Early-Universe Measurements . 24 1.6.1 Cosmic Microwave Background . 24 1.6.2 Baryonic Acoustic Oscillations . 25 2 supernovae 28 2.1 A Brief History . 28 2.2 Core-Collapse Supernovae . 30 2.3 Superluminous Supernovae . 33 2.4 Type Ia Supernovae . 33 2.4.1 Progenitors . 37 3 strong gravitational lensing 44 3.1 A Brief History . 44 3.2 Applications of Strong Lensing . 46 vii contents viii 3.3 Strong Lensing Theory . 48 3.4 Microlensing . 51 3.5 Time Delay Cosmography . 55 3.6 Mass-Sheet Degeneracy . 56 3.7 Strongly Lensed Supernovae . 59 3.7.1 Impact of gLSNe on Time Delay Cosmography . 63 3.7.2 Future Prospects . 64 ii research 67 4 the standardisation of strongly lensed type ia supernovae 68 4.1 Introduction . 68 4.2 Simulations . 72 4.3 Results and Discussion . 75 4.3.1 Microlensing Scatter . 75 4.3.2 How Many Lensed Supernovae are Standardisable? . 78 4.3.3 Lifting the Mass-Sheet Degeneracy with LSST gLSN Ia: Predic- tions for H0 ............................... 82 4.3.4 iPTF16geu................................ 83 4.4 Conclusions . 85 5 observing the earliest moments of supernovae using strong gravitational lenses 87 5.1 Introduction . 87 5.2 LSST/ZTF Populations . 91 5.2.1 gLSN Catalogues . 91 5.2.2 Trailing gLSNe Populations . 93 5.2.3 Unknown vs Known Lenses . 97 5.3 Early Phase Supernovae Models . 98 5.3.1 Type IIP Shock Breakout . 98 5.3.2 Type Ia Companion Shock Cooling . 101 5.4 Constraining SNe Ia Progenitor Populations with Early Photometry . 105 5.4.1 Constraining SN Ia Progenitor Populations with Unlensed Mon- itoring of the LSST Deep Drilling Fields . 106 5.4.2 Constraining SNe Ia Progenitor Populations with Deep Obser- vations of LSST Trailing Images . 107 contents ix 5.5 Time Delay Cosmology with Early Observations of Lensed Supernovae 108 5.6 Conclusions . 109 iii conclusions 116 6 conclusions 117 iv appendix 121 a probability theory for constraining two component progen- itor populations 122 bibliography 124 LISTOFFIGURES Figure 1 The first ‘Hubble Diagram’ used in the original determination of H0 by Hubble (1929). Plotted is the velocity-distance relation for extra-galactic ‘nebulae’, taking into account the motion of the Earth about the Sun. The black circles and solid best-fit line are from taking into account each individual nebula. The circles and dashed line come from combining the nebulae into groups. The cross represents the mean for 22 nebulae whose distances could not be measured individually. In this case, H0 is determined from the slope of the best-fit lines. 3 Figure 2 History of modern H0 measurements from 2000 - 2018. Notice tensions begin to arise between the distance ladder and ΛCDM around 2013. Figure taken from Ezquiaga and Zumalacárregui (2018), originally adapted from Beaton et al. (2016) and Freed- man (2017). Note: figure has been edited to correct ‘CPH’ to ‘CHP’. 4 x List of Figures xi Figure 3 Timeline of the ΛCDM Universe. 1) The Universe begins as a hot, dense and opaque plasma, containing baryons and pho- tons coupled together. Density fluctuations in the plasma are believed to originate from initial quantum fluctuations seeded into the structure of the Universe during a period of rapid ex- pansion called inflation (see Tsujikawa, 2003; Baumann, 2009, for reviews).