Synthetic spectra and light curves of Type Ia supernovae

To bridge the gap between hydrodynamical explosion models of thermonuclear supernovae and the observed spectra and light curves of Type Ia supernovae radiative transfer simulations in the supernova ejecta must be carried out. In this thesis a Monte Carlo code for modelling time-dependent three-dimensional spectral synthesis in chemically inhomogeneous models of Type Ia supernova ejecta is presented. Following the propagation of γ-ray photons, emitted by the radioactive decay of the nucleosynthesis products, energy is deposited in the supernova ejecta and the radiative transfer problem is solved self-consistently. Assuming a photoionization dominated plasma, the equations of ionization equilibrium are solved together with the thermal balance equation adopting an approximate treatment of excitation. Using a generalized treatment of line formation the introduction of any free parameters is avoided and the radiative transfer calculation depends only on the input model and atomic data, thus giving a maximum of predictive power for a given hydrodynamical explosion model. The operation of this code is verified using a well-known one-dimensional explosion model and the role of various effects in the radiative transfer simulation is studied. In particular, the influence of the ionization treatment and the completeness of the atomic data set used to derive the opacities are investigated. A simple two-dimensional toy model is used to quantify the effects of asphericity on the observables. Finally, the new code is applied to obtain synthetic observables for a selection of up-to-date explosion models of the hydrodynamics group at the Max Planck Institute for Astrophysics and comparisons with observational data are made. In particular, the observational signatures of different explosion mechanisms (pure deflagration and delayed-detonation) in Chandrasekhar-mass models are investigated and possible progenitor scenarios for sub-luminous SNe Ia are explored.