Radio view of a broad-line Type Ic supernova ASASSN-16fp

Abstract

We present extensive radio observations of a Type Ic supernova, ASASSN-16fp. Our data represents the lowest frequency observations of the SN beyond 1000 days with a frequency range of $0.33-25$ GHz and a temporal range of $\sim$ 8 to 1136 days post-explosion. The observations are best represented by a model of synchrotron emission from a shocked circumstellar shell initially suppressed by synchrotron self-absorption. Assuming equipartition of energy between relativistic particles and magnetic fields, we estimate the velocity and radius of the blast wave to be $v \sim 0.15c$ and $r \sim 3.4$ $\times$ $10^{15}$ cm respectively at $t_{0}$ $\sim$ 8 days post-explosion. We infer the total internal energy of the radio-emitting material evolves as $E$ $\sim$ 0.37 $\times$ $10^{47}$ (t/t$_{0}$)$^{0.65}$ erg. We determine the mass-loss rate of the progenitor star to be $\dot{M}$ $\sim$ $(0.4-3.2) \times10^{-5}$ $M_{\odot}\rm yr^{-1}$ at various epochs post-explosion, consistent with the mass-loss rate of Galactic Wolf-Rayet stars. The radio light curves and spectra show a signature of density enhancement in the CSM at a radius of $\sim$ $1.10 \times 10^{16}$ cm from the explosion center.