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We present extensive radio monitoring of a type IIb supernova (SN IIb), SN2016gkg during $t \sim$ 8$-$1429 days post explosion at frequencies $\nu \sim$0.33$-$25 GHz. The detailed radio light curves and spectra are broadlyconsistent with self-absorbed synchrotron emission due to the interaction ofthe SN shock with the circumstellar medium. The model underpredicts the fluxdensities at $t \sim$ 299 days post-explosion by a factor of 2, possiblyindicating a density enhancement in the CSM due to a non-uniform mass-loss fromthe progenitor. Assuming a wind velocity $v_{\rm w} \sim$ 200 km s$^{-1}$, weestimate the mass-loss rate to be $\dot{M} \sim$ (2.2, 3.6, 3.8, 12.6, 3.7, and5.0) $\times$ 10$^{-6}$ $M_{\odot}$ yr$^{-1}$ during $\sim$ 8, 15, 25, 48, 87,and 115 years, respectively before the explosion. The shock wave from SN2016gkg 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 shockdeceleration 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 absorptionmodel and higher shock velocities are in support of a relatively compactprogenitor for SN 2016gkg.

Radio evolution of a Type IIb supernova SN 2016gkg