Σ-D relations and main Galactic radio loops

Abstract

This paper represents the updated empirical Galactic and extragalactic Σ - D relations (relations between the surface brightness Σ and the diameter D) for supernova remnants (SNRs), with checking the connection of the main Galactic radio loops (Loop I, II, III and IV) with these relations. We present results which suggest, once again, that the radio loops may have an SNR origin. The updated relations for old SNRs have been measured to have slopes, β ≈ 2 in log-log space. The best Σ - D relations for M31 and M33 galaxies were derived and these relations are shown to be flatter (β ≲ 2) than those for Galactic SNRs alone. A Σ - D relation with 168 reliable calibrators (both Galactic and extragalactic) is derived.