The discovery of thousands of supernovae (SNe) by modern survey telescopes is allowing us to define the statistics of SN occurrence as a function of class and host galaxy properties, and is helping to facilitate the direct identification of SN progenitors. Further, we are able to routinely obtain spectra at multiple epochs that allow a SN’s temporal evolution to be followed.

Utilizing the radiative transfer code CMFGEN, we are undertaking time-dependent radiative transfer calculations for SNe that simultaneously compute multi-band light curves and spectra from approximately one day after the explosion through the photospheric phase, and into the nebular phase. The calculations are non-LTE, and allow for a multitude of atomic processes(bound-bound, bound-free, free-free, collisional, and charge exchange), and for non-thermal ex-citation and ionization from non-thermal electrons created by the degradation in energy of high energy (∼MeV) gamma-rays.

In this talk we illustrate some of the results and insights we have obtained with these calculations, with an emphasis on studies of Type Ia SNe. Despite the use of Type Ia SNe as cosmological probes, many fundamental questions about them remain unanswered. It is still un-clear, for example, whether they arise from a WD which explodes when its mass approaches the Chandrasekhar limit, or whether they arise from the merger of two WD stars. No progenitor, or companion star, was detected for the recent SN 2011fe in M101, and this is providing tight limits on SN Ia models. The superb data being obtained for this object are also providing important new constraints and insights.