Radio evolution of a Type IIb supernova SN 2016gkg

TL;DR

This study presents detailed radio observations of supernova SN 2016gkg, revealing shock interaction with circumstellar material, variable mass-loss rates, and a relatively compact progenitor, advancing understanding of supernova environments.

Contribution

First extensive radio monitoring of SN 2016gkg, providing insights into shock dynamics, circumstellar interaction, and progenitor characteristics with detailed modeling.

Findings

Radio emission consistent with synchrotron shock interaction

Evidence of non-uniform circumstellar medium density

Estimated progenitor's compact size and variable mass-loss history

Abstract

We present extensive radio monitoring of a type IIb supernova (SN IIb), SN 2016gkg during $t \sim$ 8$-$1429 days post explosion at frequencies $\nu \sim$ 0.33$-$25 GHz. The detailed radio light curves and spectra are broadly consistent with self-absorbed synchrotron emission due to the interaction of the SN shock with the circumstellar medium. The model underpredicts the flux densities at $t \sim$ 299 days post-explosion by a factor of 2, possibly indicating a density enhancement in the CSM due to a non-uniform mass-loss from the progenitor. Assuming a wind velocity $v_{\rm w} \sim$ 200 km s$^{-1}$, we estimate the mass-loss rate to be $\dot{M} \sim$ (2.2, 3.6, 3.8, 12.6, 3.7, and 5.0) $\times$ 10$^{-6}$ $M_{\odot}$ yr$^{-1}$ during $\sim$ 8, 15, 25, 48, 87, and 115 years, respectively before the explosion. The shock wave from SN 2016gkg is expanding from $R \sim$ 0.5 $\times$ 10$^{16}$ to 7 $\times$ 10$^{16}$ cm during $t \sim$ 24$-$492 days post-explosion indicating a shock deceleration index, $m$ $\sim$ 0.8 ($R \propto t^m$), and mean shock velocity $v \sim$ 0.1c. The radio data being inconsistent with free-free absorption model and higher shock velocities are in support of a relatively compact progenitor for SN 2016gkg.