Supernovae and their circumstellar environment

Summary

Abstract

Some supernovae are visible for several years past explosion. The main energy source for this sustained emission conies from the supernova shock interacting with the remnant of the stellar wind of the progenitor star. We review the available evidence for this picture and exclude other power sources on the basis of the radiated energies. We also discuss a group of supernovae which display narrow emission lines with high fluxes in their spectra and very slowly declining optical light curves. These observations can most readily be explained as being due to interaction with a very dense medium close to the supernova.

Introduction

A variety of supernova interactions with circumstellar material (CSM) has been observed to date. The best, and most direct, example is the ring of emission around SN 1987A (Jakobsen et al. 1991). This material has been ionized by the UV and soft X-ray flash of the shock breakout at the surface of the supernova (Fransson et al. 1989, Lundqvist & Fransson 1989). The density enhancement in the ring is caused by the interaction of the fast blue supergiant wind colliding with the slow red supergiant wind of a previous epoch (Blondin & Lundqvist 1993). In the case of SN 1993J, the early detection of radio and X-ray emission, in combination with narrow emission lines in the UV and optical, are indicative of interaction with the CSM. Blue optical continua, X-ray detection at early phases, as well as the UV emission have been proposed as characteristics of a shock in the CSM around SN 1979C (Fransson 1984).