Radio and X-rays From SN 2013df Enlighten Progenitors of Type IIb Supernovae

TL;DR

This study analyzes radio and X-ray data of SN 2013df, revealing insights into its progenitor's mass loss, shock properties, and spectral evolution, and compares it with similar supernovae like SN 1993J.

Contribution

It provides the first detailed multiband modeling of SN 2013df, highlighting deviations from energy equipartition and linking optical emission with radio and X-ray characteristics.

Findings

SN 2013df exhibits a soft-to-hard spectral evolution in radio emission.

Estimated mass loss rate of the progenitor is approximately 8 x 10^{-5} solar masses per year.

Shock wave speed is about 0.07 times the speed of light, typical for radio supernovae.

Abstract

We present radio and X-ray observations of the nearby Type IIb Supernova 2013df in NGC4414 from 10 to 250 days after the explosion. The radio emission showed a peculiar soft-to-hard spectral evolution. We present a model in which inverse Compton cooling of synchrotron emitting electrons can account for the observed spectral and light curve evolution. A significant mass loss rate, $\dot{M} \approx 8 \times 10^{-5}\,\rm M_{\odot}/yr$ for a wind velocity of 10 km/s, is estimated from the detailed modeling of radio and X-ray emission, which are primarily due to synchrotron and bremsstrahlung, respectively. We show that SN 2013df is similar to SN 1993J in various ways. The shock wave speed of SN 2013df was found to be average among the radio supernovae; $v_{sh}/c \sim 0.07$. We did not find any significant deviation from smooth decline in the light curve of SN 2013df. One of the main results of our self-consistent multiband modeling is the significant deviation from energy equipartition between magnetic fields and relativistic electrons behind the shock. We estimate $\epsilon_{e} = 200 \epsilon_{B}$. In general for Type IIb SNe, we find that the presence of bright optical cooling envelope emission is linked with free-free radio absorption and bright thermal X-ray emission. This finding suggests that more extended progenitors, similar to that of SN 2013df, suffer from substantial mass loss in the years before the supernova.