A New Look at Radio Supernova Remnants

Abstract

Catalogues are presented of radio supernova remnants in both Large (LMC) and Small (SMC) Magellanic Clouds together with maps of the LMC remnants prepared at a frequency of 843 MHz and with a resolution of 43 x 45 arcsec. The 38 confirmed remnants are believed to represent a reasonably complete sample for diameters less than about 40 pc although the LMC catalogue is probably very incomplete for larger diameters. The supernova remnants (SNRs) are compared with the Galactic remnants in the catalogue of Clark and Caswell (1976) and they are found to be similar in many ways. In particular a distance scale derived from the Cloud SNRs reproduces well the mean distances of directly measured Galactic calibrators. The usual model of a SNR expanding adiabatically from a small diameter is not supported by the statistics of the numberdiameter relation which suggest that rapid expansion up to quite large diameters is common. The physical implications are discussed. A supernova rate of about four per century is derived for the Galaxy and about one per century for the two Magellanic Clouds combined.