Circumstellar matter and the nature of the SN1987A progenitor star

Abstract

The radio observations of the supernova SN1987A1,2 can be inter-preted in terms of its interaction with circumstellar matter. The early turn-on of the radio emission implies a relatively low density circumstellar medium, with Ṁ/Vw = 8.8 × 10−6 Mo yr−1 per (550 km s−1) where Ṁ is the mass loss rate from the progenitor star and Vw is the wind velocity. The optical properties of the supernova imply that the progenitor star had a smaller radius than that of a typical type II supernova progenitor. The mass loss properties are consistent with this hypothesis. We predict the thermal X-ray luminosity of the supernova and note that it is below the current upper limit3. A bright infrared dust echo is not expected, although a weak echo from an earlier mass loss phase is possible. Weak ultraviolet emission lines from circumstellar gas may be visible. Although the circumstellar density is low, it is possible that the progenitor star did lose a substantial fraction of its mass prior to the supernova explosion.