Abstract

Radio supernovae (RSNe) are an excellent, means of probing the circumstellar matter around, and therefore the winds from, supernova (SN) progenitor stars or stellar systems. The observed radio synchrotron emission is best described by the Chevalier model, which involves the generation of relativistic electrons and enhanced magnetic fields through the SN shock interacting with a relatively high-density circumstellar envelope, which is presumed to have been established through mass loss in the late stages of stellar evolution. From the Chevalier model, modified to include a mixed, internal, nonthermal emission/thermal absorption component, we can use the observed radio emission from these SNe to derive physical properties, including the ratio of the mass-loss rate to the stellar wind speed, which determines the circumstellar matter density. Assuming a value for the wind speed then allows us to determine a mass-loss rate for the star responsible for the circumstellar matter and to estimate its mass. For Type II RSNe, this mass loss is assumed to originate from the presupernova star itself, while for Type 1b/c RSNe, the stellar wind is assumed to be from the binary companion to the SN progenitor. Extreme examples of progenitor winds are found for unusual Type II RSNe, for which radio properties indicate that the matter around these SNe resulted from very high mass-loss rates in the late stages of the evolution of very massive stars. Additionally, we have observed deviations from the standard model, probably providing evidence for inhomogeneities in the circumstellar matter density and possibly indicating the presence of stellar pulsations or an interacting binary companion.