Radio observations of historical, extragalactic supernovae

Abstract

VLA maps of the galaxy M83 (NGC 5236) at b and 20 cm reveal the presence of both non-thermal and thermal sources, lying predominantly along the inner edges of the optical spiral arms. A radio source coincident with the optical position of supernova 1957d is found to have a non-thermal spectrum; thus SN 1957d is confirmed as the first supernova of intermediate-age (~ 10-300 years) to be detected at any wavelength. A second non-thermal source is tentatively identified with supernova 1950b, pending the measurement of a precise optical position of the supernova. Two other non-thermal sources lying along the inner edges of the spiral arms are likely to be the remnants of supernovae which were not seen optically. All four sources have monochromatic luminosities comparable to that of Cas A. A composite “radio light curve” for supernovae and young supernova remnants of known age is presented and discussed.