Early- and late-time observations of SN 2008ha: Additional constraints for the progenitor and explosion

We present a new maximum-light optical spectrum of the extremely low luminosity and exceptionally low-energy TypeIa supernova (SNIa) 2008ha, obtained one week before the earliest published spectrum. Previous observations of SN2008ha were unable to distinguish between a massive star and white dwarf (WD) origin for the SN. The new maximum-light spectrum, obtained one week before the earliest previously published spectrum, unambiguously shows features corresponding to intermediate mass elements, including silicon, sulfur, and carbon. Although strong silicon features are seen in some core-collapse SNe, sulfur features, which are a signature of carbon/oxygen burning, have always been observed to be weak in such events. It is therefore likely that SN2008ha was the result of a thermonuclear explosion of a carbon-oxygen WD. Carbon features at maximum light show that unburned material is present to significant depths in the SNejecta, strengthening the case that SN2008ha was a failed deflagration. We also present late-time imaging and spectroscopy that are consistent with this scenario.