Abstract
ABSTRACT We report evidence for excess blue light from the Type Ia supernova (Sn Ia) SN 2012cg at 15 and 16 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 normal 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 Δ m 15 ( B ) = 0.86 ± 0.02 ?> . Our data set is extensive, with photometry in seven filters from five 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 favors a main-sequence companion of about six 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.
Highlights
It is widely accepted that Type Ia supernovae (SN Ia) are the thermonuclear explosions of carbon–oxygen white dwarfs, and many of them appear to explode near the Chandrasekhar mass (MCh; e.g., Hillebrandt & Niemeyer 2000), though they may arise from progenitors of other masses as well (e.g., Scalzo et al 2014)
In order to test the null-hypothesis, i.e., whether the entire light curves (LC) could be fit with a single t n model without any excess flux, we extended the fitting range to −18 days, all data in between −18 and −8 days were fit by the more flexible t n model
We find excess luminosity at −16 and −15 days in the LCs of SN Ia 2012cg
Summary
It is widely accepted that Type Ia supernovae (SN Ia) are the thermonuclear explosions of carbon–oxygen white dwarfs, and many of them appear to explode near the Chandrasekhar mass (MCh; e.g., Hillebrandt & Niemeyer 2000), though they may arise from progenitors of other masses as well (e.g., Scalzo et al 2014). Individual SN Ia that are found very nearby or very early provide high quality data that may be unavailable to larger surveys Analyses of such SN Ia have revealed an interesting amount of diversity, but no clear signs of shock interaction with a companion. Schaefer & Pagnotta (2012) determined that SNR 0509–67.5 in the Large Magellanic Cloud contains no candidates for the companion star to deep limits They claim to eliminate all previously published singledegenerate models for this SN Ia. Zheng et al (2013) showed that measurements of SN 2013dy, obtained only a few hours after the estimated time of the explosion, do not reveal any evidence for interaction.
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