SN~2012cg: Evidence for Interaction Between a Normal Type Ia Supernova and a Non-Degenerate Binary Companion

Kavli Affiliate: Kaisey Mandel

| First 5 Authors: G. H. Marion, Peter J. Brown, Jozsef Vinkó, Jeffrey M. Silverman, David J. Sand

| Summary:

We report evidence for excess blue light from the Type Ia supernova SN 2012cg
at fifteen and sixteen days before maximum B-band brightness. The emission is
consistent with predictions for the impact of the supernova on a non-degenerate
binary companion. This is the first evidence for emission from a companion to a
SN Ia. Sixteen days before maximum light, the B-V color of SN 2012cg is 0.2 mag
bluer than for other normal SN~Ia. At later times, this supernova has a typical
SN Ia light curve, with extinction-corrected M_B = -19.62 +/- 0.02 mag and
Delta m_{15}(B) = 0.86 +/- 0.02. Our data set is extensive, with photometry in
7 filters from 5 independent sources. Early spectra also show the effects of
blue light, and high-velocity features are observed at early times. Near
maximum, the spectra are normal with a silicon velocity v_{Si} = -10,500$ km
s^{-1}. Comparing the early data with models by Kasen (2010) favors a
main-sequence companion of about 6 solar masses. It is possible that many other
SN Ia have main-sequence companions that have eluded detection because the
emission from the impact is fleeting and faint.

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