paper

Red vs Blue: Early observations of thermonuclear supernovae reveal two distinct populations?

arXiv:1807.07576 · doi:10.3847/2041-8213/aadd46

Abstract

We examine the early phase intrinsic color evolution of a dozen Type~Ia supernovae discovered within three days of the inferred time of first light () and have color information beginning within 5 days of . The sample indicates there are two distinct early populations. The first is a population exhibiting blue colors that slowlybevolve, and the second population exhibits red colors and evolves more rapidly. We find that the early-blue events are all 1991T/1999aa-like with more luminous slower declining light curves than those exhibiting early-red colors. Placing the first sample on the Branch diagram (i.e., ratio of \ion{Si}{2} 5972, 6355 pseudo-Equivalent widths) indicates all blue objects are of the Branch Shallow Silicon (SS) spectral type, while all early-red events except for the 2000cx-like SN~2012fr are of the Branch Core-Normal (CN) or CooL (CL) type. A number of potential processes contributing to the early emission are explored, and we find that, in general, the viewing-angle dependance inherent in the companion collision model is inconsistent with all SS objects with early-time observations being blue and exhibiting an excess. We caution that great care must be taken when interpreting early-phase light curves as there may be a variety of physical processes that are possibly at play and significant theoretical work remains to be done.

arXiv commentAccepted to ApJ Letters. Replaced with updated manuscript including responses to referee's comments

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