Shock kinematics: a promising avenue to understanding Type-Ia supernovae
Creators: name: Arunachalam, Prasiddha
Publisher: name: No Publisher Supplied
Year: 2023

description: Type Ia supernovae (SNe Ia) have been the lynchpins behind the discovery of the accelerated expansion of the universe, a revelation that has fundamentally changed our perception of the universe, and deservedly recognized with the Nobel prize in 2011. Their critical role in cosmology rests on the evidence that these explosions are very uniform in brightness, and can hence be used to estimate cosmological distances. SNe Ia also recycle the material in stars back into the interstellar medium (ISM), accelerate cosmic rays, and contribute significantly to the chemical enrichment of galaxies by producing most of the iron and iron-group elements in the universe. However, despite this versatility, there are several unknowns surrounding the physics governing these explosions. Unlike core-collapse supernovae, which have clear observational evidence for arising in massive star systems, direct evidence for the SNe Ia progenitor system does not exist. The well-accepted theory, however, is that SN Ia arise in binary systems of stars, where at least one is a white-dwarf (WD). But what type of progenitor systems form the binary pair? Why are these explosions so uniform? And what is the explosion mechanism? These are some fundamental questions that do not have clear answers. One promising avenue to answer these questions comes from supernova remnants (SNRs), which are the aftermaths of supernovae (anywhere from few hundred to several thousand years after the explosion), formed from the interaction of the debris of the exploding star with the ISM. In this dissertation, I provide a systematic approach to understand and measure the explosion properties and environment of the parent supernovae of young Ia SNRs using kinematic information from their shocks, namely- the blast wave from the explosion, or the forward shock (FS), and a reaction wave formed from the expanding material being slowed down by the ISM, or the reverse shock (RS). For young SNRs, these shocks are actively evolving, either sweeping up the ISM material on their way out, or heating the expanding material as they plough back into the ejecta. Along the way, we measure accurate proper motions and locations of the FS for two SNRs in the Large Magellanic Cloud (LMC) namely SNR 0509−67.5 and SNR 0519−69.0 using the Hubble Space Telescope. Next, we present a Monte Carlo Markov Chain (MCMC) framework that utilizes the proper motion and location measurements to infer fundamental parameters governing the parent explosion. We also emphasize the importance of the [Fe XIV] coronal emission line, and discuss the Southern African Large Telescope (SALT) project we designed to search for [Fe XIV] emission from young Ia SNRs in the LMC. The coronal [Fe XIV] emission can be used as a proxy for the RS location, information which, when utilized in our MCMC framework, has resulted in the first data-informed constraints on critical explosion quantities like the explosion energy. Finally, SNR shocks are known to be sites that accelerate galactic cosmic rays (CRs), whose origins remain one of the longest-standing unsolved problems in astrophysics. For SNR 0509−67.5, we interpret the MCMC parameter fits in the context of CR acceleration, and comment on the efficiency of particle acceleration at the SNR’s FS. Our MCMC framework shows great promise in terms of its applicability to many young remnants in the Milky Way and nearby galaxies, and to understanding the specifics of individual SNe Ia explosions. With its applicability, we now have the opportunity to bring together and address fundamental questions in astrophysics surrounding SNe Ia: the progenitor problem, cosmic ray acceleration in shocks, and the properties of the parent supernova.