Modelling of the radio burst from SN1987A

Abstract

Observations at Australian observatories¹ showed that radio emission from SN1987A in the Large Magellanic Cloud² reached a peak of ~100 mJy at frequencies of ~ 1 GHz within three days of the optical rise and then declined on a similar timescale. This behaviour is different from that observed from previous extragalactic type II radio supernovae³ where the peak luminosity is two to three orders of magnitude greater and the emission rises tens or even hundreds of days after the supernova event and then decays with a timescale of years. Here we propose that the radio emission mechanism for SN1987A is the same as that proposed for previous type II supernova⁴, namely, synchrotron emission from a thin shell near the edge of the expanding ejecta. The differences are mainly due to the absence of a thick circumstellar envelope around the progenitor star, Sk –69 202, at least in the line of sight to the supernova. We discuss several possible models for the emission and absorption processes and set limits on the density of a circumstellar envelope.