Search for radio emission from the young supernova remnants in NGC6946

Abstract

Although recent supernovae in our own Galaxy are among the brightest radio sources in the sky—particularly Cas A and the Crab Nebula (500-1,000 yr post-outburst)—the evolution of their radio emission from outburst to the present is, of course, unknown. Unless and until we have the opportunity to study a new galactic supernova, our information on the immediate post-outburst radio properties of supernova remnants must come from studies of identified supernovae in external galaxies. NGC6946 is one galaxy in which such a study is particularly favourable both because supernovae occur frequently in this galaxy—four supernovae have been identified since 1917—and because of its relative proximity. Two previous searches have failed to detect radio emission from these remnants^1,2. However, the greater sensitivity presently available at radio wavelengths allows us not only to conduct a more sensitive search for these remnants but also to determine whether the radio emission has brightened since the last surveys ∼ 5 yr ago.