UC Berkeley

When a supernova explodes within a dense circumstellar environment, it creates a highly energetic shockwave that can be observed across the entire electromagnetic spectrum. The shockwave emission can be used as an observational probe to infer the properties of the circumstellar medium (CSM), and learn about how the progenitor star lived out its final moments before death. Numerous explanations have been proposed to explain the CSM, with each physical model varying in the amount of expelled mass, its spatial extent, and geometry. Due to the inherent difficulty in modeling the shock emission from circumstellar interaction, simplified analytic and numerical models are widely used to interpret observational data. However, the assumptions made in these simplified models, their range of applicability, and their ability to accurately infer physical quantities is not clear. In this thesis, I have extended the Monte Carlo radiative transfer code Sedona with advanced multi-physics simulation capabilities, including one-dimensional finite-volume arbitrary Lagrangian-Eulerian hydrodynamics, inline multi-group non-LTE opacities, and non-thermal electron populations. I leverage these capabilities to perform extensive radiation hydrodynamics simulations of interacting supernovae, and construct a broad theoretical framework with which to interpret their resulting light curves. I find that CSM interaction can produce a wide range of light curve durations and luminosities, with timescales ranging from hours to months. I demonstrate their viability in powering a broad range of unusual supernovae. In particular, I show how CSM interaction is a plausible explanation for the recently-discovered class of fast blue optical transients, and constrain the CSM properties inferred for this type. For the specific case of the Type II subclass of interacting supernovae, I perform non-equilibrium multi-group radiation hydrodynamics simulations to construct time-dependent panchromatic radio to X-ray spectral energy distributions of the combined supernova and shock emission. I find that analytic expectations used in the literature disagree with the numerical light curves due to an evolving non-thermal electron energy population with contributions from both the forward and reverse shocks, compounded by the effects of inverse Compton scattering and photo-absorption by a cold dense shell.