Ryle Telescope observations of SN 1993J

Summary

Abstract

We present observations of SN 1993J made with the Ryle Telescope, Cambridge, UK, at 15.25 GHz. These show a sharp switch-on of the radio emission about eight days after the supernova explosion, with the emission then brightening at an approximately constant rate for the next month. The emission peaked about 75 days after the explosion, and then showed a gradual decline, with variations on the timescale of weeks. The long, steady rise in emission and the sharp switch-on do not fit with expected radio emission from ‘mini-shell’ models of radio supernovae.

Introduction

The detection of SN 1993J in NGC3031 (≡M81) by F. Garcia on March 28.86 was reported in an IAU Circular by Ripero (1993) on March 30. This was the nearest supernova (SN) detected in the northern hemisphere since SN 1937C, and it has been, and will be, studied at many wavelengths in more detail than any other SN except SN 1987A in the LMC. SN 1993J showed hydrogen lines in its early spectra, and was initially thought to be a type II SN, but subsequently its spectra developed to resemble those of type Ib SN. Thus it has been classed as a peculiar type IIb SN (Filippenko & Matheson 1993), and it is thought to be the result of the explosion of a massive star which has almost lost its outer hydrogen-rich envelope.