Radio Emission from Supernovae in the Very Early Phase: Implications for the Dynamical Mass Loss of Massive Stars

TL;DR

This paper explores how early radio emissions, especially in the millimeter range, from supernovae can reveal the presence of dense, confined circumstellar material caused by rapid mass loss in massive stars shortly before explosion.

Contribution

It demonstrates that millimeter synchrotron emission can serve as a sensitive probe of confined CSM and predicts its detectability with ALMA, providing new insights into pre-supernova mass loss.

Findings

Millimeter synchrotron emission is detectable from supernovae with confined CSM.

Such emission can distinguish different CSM density profiles.

Secondary electrons significantly contribute to the emission within tens of days post-explosion.

Abstract

Recent high-cadence transient surveys and rapid follow-up observations indicate that some massive stars may dynamically lose their own mass within decades before supernovae (SNe). Such a mass-loss forms `confined' circumstellar medium (CSM); a high density material distributed only within a small radius ($\lesssim 10^{15}$ cm with the mass-loss rate of 0.01 $\sim 10^{-4} M_\odot$ yr$^{-1}$). While the SN shock should trigger particle acceleration and magnetic field amplification in the `confined' CSM, synchrotron emission may be masked in centimeter wavelengths due to free-free absorption; the millimeter range can however be a potential new window. We investigate the time evolution of synchrotron radiation from the system of a red super giant surrounded by the `confined' CSM, relevant to typical type II-P SNe. We show that synchrotron millimeter emission is generally detectable, and the signal can be used as a sensitive tracer of the nature of the `confined' CSM; it traces different CSM density parameter space than in the optical. Furthermore, our simulations show that the `confined' CSM efficiently produces secondary electrons and positrons through proton inelastic collisions, which can become main contributors to the synchrotron emission in several ten days since the SN. We predict that the synchrotron emission is detectable by ALMA, and suggest that it will provide a robust evidence of the existence of the `confined' CSM.