The progenitor and early evolution of the Type IIb SN 2016gkg

TL;DR

This paper presents early observations and analysis of the Type IIb supernova 2016gkg, revealing its double-peaked light curve, spectral features, and progenitor characteristics through photometry, spectroscopy, and archival imaging.

Contribution

It provides the first detailed early evolution analysis of SN 2016gkg, including progenitor identification and modeling of its temperature evolution, highlighting differences from similar supernovae.

Findings

SN 2016gkg exhibited a double-peaked light curve.

Progenitor star estimated to be 15-20 solar masses.

Progenitor radius modeled as 48-124 solar radii.

Abstract

We report initial observations and analysis on the Type IIb SN~2016gkg in the nearby galaxy NGC~613. SN~2016gkg exhibited a clear double-peaked light curve during its early evolution, as evidenced by our intensive photometric follow-up campaign. SN~2016gkg shows strong similarities with other Type IIb SNe, in particular with respect to the \he~emission features observed in both the optical and near infrared. SN~2016gkg evolved faster than the prototypical Type~IIb SN~1993J, with a decline similar to that of SN~2011dh after the first peak. The analysis of archival {\it Hubble Space Telescope} images indicate a pre-explosion source at SN~2016gkg's position, suggesting a progenitor star with a $\sim$mid F spectral type and initial mass $15-20$\msun, depending on the distance modulus adopted for NGC~613. Modeling the temperature evolution within $5\,\rm{days}$ of explosion, we obtain a progenitor radius of $\sim\,48-124$\rsun, smaller than that obtained from the analysis of the pre-explosion images ($240-320$\rsun).