Constraints on the Progenitor of SN 2016gkg From Its Shock-Cooling Light Curve

TL;DR

This study uses detailed early light-curve data and analytical models to constrain the size and envelope mass of SN 2016gkg's progenitor, providing insights into its nature and limitations of current models.

Contribution

First detailed multi-band, intranight-cadence observations of SN 2016gkg's early light curve and analytical modeling to estimate progenitor properties.

Findings

Progenitor radius estimated at 25-140 solar radii.

Extended envelope mass estimated at 0.02-0.3 solar masses.

Shock-cooling model radii are on the lower end compared to pre-explosion imaging.

Abstract

SN 2016gkg is a nearby Type IIb supernova discovered shortly after explosion. Like several other Type IIb events with early-time data, SN 2016gkg displays a double-peaked light curve, with the first peak associated with the cooling of a low-mass extended progenitor envelope. We present unprecedented intranight-cadence multi-band photometric coverage of the first light-curve peak of SN 2016gkg obtained from the Las Cumbres Observatory Global Telescope network, the Asteroid Terrestrial-impact Last Alert System, the Swift satellite and various amateur-operated telescopes. Fitting these data to analytical shock-cooling models gives a progenitor radius of ~25-140 solar radii with ~2-30 x 10^-2 solar masses of material in the extended envelope (depending on the model and the assumed host-galaxy extinction). Our radius estimates are broadly consistent with values derived independently (in other works) from HST imaging of the progenitor star. However, the shock-cooling model radii are on the lower end of the values indicated by pre-explosion imaging. Hydrodynamical simulations could refine the progenitor parameters deduced from the shock-cooling emission and test the analytical models.