Type IIP supernova SN 2016X in radio frequencies

TL;DR

This study presents radio observations of supernova SN 2016X during its plateau phase, modeling its shockwave and progenitor mass-loss, revealing a non-constant expansion and electron cooling effects, with implications for supernova physics.

Contribution

First detailed radio analysis of SN 2016X during plateau phase, modeling shock dynamics and progenitor mass-loss, and examining energy partitioning in the shockwave.

Findings

Shockwave expands with a power-law index m=0.76.

Progenitor mass-loss rate is approximately 7.8 x 10^{-7} M_sun/yr.

Spectral steepening caused by electron cooling via inverse Compton.

Abstract

Context: The study of radio emission from core-collapse supernovae (SNe) probes the interaction of the ejecta with the circumstellar medium (CSM) and reveals details of the mass-loss history of the progenitor. Aims: We report observations of the type IIP supernova SN\,2016X during the plateau phase, at ages between 21 and 75 days, obtained with the Karl G. Jansky Very Large Array (VLA) radio observatory. Methods: We modelled the radio spectra as self-absorbed synchrotron emission, and we characterised the shockwave and the mass-loss rate of the progenitor. We also combined our results with previously reported X-ray observations to verify the energy equipartition assumption. Results: The properties of the shockwave are comparable to other type IIP supernovae. The shockwave expands according to a self-similar law $R \propto t^m$ with $m=0.76 \pm 0.08$, which is notably different from a constant expansion. The corresponding shock velocities are approximately 10700 - 8000 km s$^{-1}$ during the time of our observations. The constant mass-loss rate of the progenitor is $\dot{M}=$ (7.8 $\pm$ 0.9)\,$\times 10^{-7} \alpha^{-8/19} (\epsilon_B/0.1)^{-1} M_{\odot}$ yr$^{-1}$, for an assumed wind velocity of 10 km s$^{-1}$. We observe spectral steepening in the optically thin regime at the earlier epochs, and we demonstrate that it is caused by electron cooling via the inverse Compton effect. We show that the shockwave is characterised by a moderate deviation from energy equipartition by a factor of $\epsilon_e / \epsilon_B \approx 28$, being the second type IIP supernova to show such a feature.