The Light Curves and Spectra of Supernova Explosions: Multi- Dimensional Time-Dependent Monte Carlo Radiative Transfer Calculations Daniel Kasen, Johns Hopkins University

While the violent disruption of a star in a supernova explosion lasts only a few minutes, the ejected stellar material (much of it newly radioactive) continues to shine for several months with a luminosity detectable billions of light years away. Empirical correlations exist between the intrinsic brightness of the event and its temporal evolution (light curve), making supernovae a useful tool for measuring cosmological distances and mapping the expansion history of the universe. 3-Dimensional multi-physics simulations are now illuminating the physics (e.g., hydrodynamics and turbulent nuclear combustion) of the supernova explosion itself, but must be further coupled to radiative transfer codes to predict the observable emission. Here we discuss Monte Carlo techniques for addressing the time-dependent radiative transfer problem in 3-dimensional, rapidly expanding atmospheres. Our SEDONA code calculates angle dependent light curves, spectra, and spectropolarization of model supernovae which we compare directly to astronomical observations. The code includes a detailed treatment of radioactive heating and an iterative solution for the gas temperature through energy balance. While the approximation of local thermodynamic equilibrium (LTE) is a useful computational expedient, the code also allows for the direct solution of the non-LTE matrix rate equations to determine the gas excitation/ ionization state. The SEDONA code is parallelized using a hybrid of MPI and openMP and has been run on high-performance computing systems using up to 1024 processors.