The circumstellar gas around SN 1987A and SN 1993J

Summary

Abstract

The observational evidence for circumstellar gas around SN 1987A and SN 1993J is discussed along with interpretations of these observations. For SN 1987A we focus on its ring and for SN 1993J we mainly concentrate on its radio and N V λ 1240 emission.

Introduction

The circumstellar gas (CSG) around supernovae (SNe) provides information on the mass loss history of the dying star. When the SN explodes, the CSG is ionized by the radiation from both the SN and the gas shocked by the expanding ejecta. By looking at spectral signatures from the ionized CSG at increasingly large radii, we may peer deeper and deeper back through time into the mass loss history of the pre-SN. The recent bright and well-studied Type II SNe 1987A and 1993J have given us an unprecedented chance of doing so. Here we briefly discuss the CSG of these two SNe.

SN 1987A

Light curves for the narrow UV emission lines from SN 1987A (Sonneborn et al. 1994) show that the emission starts ∼ 70 days after the outburst with a roughly linear increase in strength until day ∼ 400, followed by a gradual decline up to day ∼ 1000 when the lines start to fall below detectability. In the optical there is very good information on the spatial flux distribution from observations with the NTT (Wampler et al. 1990; Wang & Wampler 1992) and the HST (Jakobsen et al. 1991; Plait et al. 1994); the emission mainly comes from a patchy, elliptically shaped ring with semimajor and semiminor axes of ∼ 0.830 (corresponding to ∼ 6.2 × 10¹⁷ cm at 50 kpc) and ∼ 0.605 arcsec, respectively.