http://arxiv.org/abs/1807.07576
We examine the early phase intrinsic $(B-V){0}$ color evolution of a dozen Type~Ia supernovae discovered within three days of inferred time of first light ($t{first}$) and have $(B-V)0$ color information beginning within 5 days of $t{first}$. The sample indicates there are two distinct early populations. The first is a population exhibiting blue colors that slowly evolve, and the second population exhibits red colors and evolves more rapidly. Placing the first sample on the Branch diagram (i.e., ratio of \ion{Si}{2} $\lambda\lambda$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 peculiar SN~2012fr– are of the Branch Core-Normal (CN) or CooL (CL) type. Inspection of their light curves indicate early-blue events are typically more luminous with slower declining light curves than those exhibiting early-red colors.A number of potential processes contributing to the early emission are explored, and we caution that great care must be taken when interpreting early-phase light curves.
M. Stritzinger, B. Shappee, A. Piro, et. al.
Mon, 23 Jul 18
32/48
Comments: Submitted to ApJ Letters on June 27, 7 pages, including 4 figures and 1 table. Constructive comments are most welcome