Title: Understanding Type Ia Supernova Spectra

Abstract: 

Some stars end their lives in spectacular explosive deaths called supernovae. We understand this process happens in predominantly two ways, the collapse of the stellar cores in massive stars or the thermonuclear explosions of white dwarf (WD) stars at or near the Chandrasekhar mass (Mch). This thesis focuses on the thermonuclear supernovae, called Type Ia (SNe Ia). Despite the decades of theoretical work and observational constraints of SNe Ia coming from WDs, the nature of the progenitor systems and explosion scenario is unknown. The fundamental questions still unanswered are, "Do SNe Ia come from WDs with non-degenerate companions or WD companions?'' and "How/why do WDs explode?'' To investigate the nature of SNe Ia, I performed time series radiative transfer calculations of various hydrodynamic ejecta models. Since we cannot observe the explosion itself, spectra are tools to probe the progenitor properties. My aims were to determine ejecta mass diagnostics of SNe Ia by comparing radiative transfer calculations of four hydrodynamic ejecta models in the mass range of 1.0--1.7 Mch. Because nebular spectra are dominated by emission lines from the innermost part of the ejecta, I also investigate the physics of nebular SN Ia spectra to determine the properties of the progenitor and explosion physics. The luminosity of SNe Ia is powered by the radioactive decay of 56Ni and subsequent decay of 56Co. Gamma-rays produced during these decays scatter in the ejecta before either escaping or being absorbed. This thesis contains work modeling the gamma-ray flux and energy deposition function. To date, SN2014J is the only SN Ia with gamma-ray observations. Detailed gamma-ray modeling will be compared to all future observations to add additional constraints on the production of 56Ni and ejecta density structure.