On the Progenitor of the Type IIb Supernova 2016gkg

TL;DR

This paper identifies and characterizes the progenitor star of supernova 2016gkg using pre- and post-explosion imaging, revealing it to be a likely binary system with properties consistent with models and early light curve data.

Contribution

First detection of a supernova progenitor in pre-explosion HST images, combined with early light curve analysis to constrain progenitor properties and explosion timing.

Findings

Progenitor likely an A0Ia star with T=9500 K and log(L/Lsun)=5.15.

Progenitor appears more consistent with binary evolution models.

Explosion date determined as 20.15 September 2016, with progenitor radius log(R/Rsun)=2.41.

Abstract

We present a detection in pre-explosion Hubble Space Telescope (HST) imaging of a point source consistent with being the progenitor star of the Type IIb supernova (SN IIb) 2016gkg. Post-explosion imaging from the Keck Adaptive Optics system was used to perform relative astrometry between the Keck and HST imaging. We identify a single point source in the HST images coincident with the SN position to 0.89-sigma. The HST photometry is consistent with the progenitor star being an A0Ia star with T=9500 K and log (L/Lsun)=5.15. We find that the SN 2016gkg progenitor star appears more consistent with binary than single-star evolutionary models. In addition, early-time light curve data from SN 2016gkg revealed a rapid rise in luminosity within ~0.4 days of non-detection limits, consistent with models of the cooling phase after shock break-out. We use these data to determine an explosion date of 20.15 September 2016 and progenitor star radius of log (R/Rsun)=2.41, which agrees with photometry from the progenitor star. Our findings are also consistent with detections of other SNe IIb progenitor stars, although more luminous and bluer than most other examples.