Heating from free-free absorption and the mass-loss rate of the progenitor stars to supernovae

TL;DR

This paper presents a method to directly determine the mass-loss rate of supernova progenitors using free-free absorption observations, reducing model uncertainties and enabling consistency checks.

Contribution

It introduces a self-consistent approach to measure mass-loss rates from free-free optical depth, distinguishing heating mechanisms and improving accuracy.

Findings

Mass-loss rate of SN 1993J progenitor estimated at ~10^(-5) solar masses/year.

Free-free heating explains observed absorption in SN 1993J.

Method allows model-independent mass-loss rate determination.

Abstract

An accurate determination of the mass-loss rate of the progenitor stars to core-collapse supernovae is often limited by uncertainties pertaining to various model assumptions. It is shown that under conditions when the temperature of the circumstellar medium is set by heating due to free-free absorption, observations of the accompanying free-free optical depth allow a direct determination of the mass-loss rate from observed quantities in a rather model independent way. The temperature is determined self-consistently, which results in a characteristic time dependence of the free-free optical depth. This can be used to distinguish free-free heating from other heating mechanisms. Since the importance of free-free heating is quite model dependent, this also makes possible several consistency checks of the deduced mass-loss rate. It is argued that the free-free absorption observed in SN 1993J is consistent with heating from free-free absorption. The deduced mass-loss rate of the progenitor star is, approximately, 10^(-5) solar masses per year for a wind velocity of 10 km/s.