Supernova remnants resembling the Crab nebula

Recent observations show that at least eight radio supernova remnants have centrally concentrated brightness distributions similar to that of the Crab nebula. We have noticed a remarkable general property of these remnants – in every instance the major axis of the radio isophotes lies roughly parallel to the galactic plane; a possible explanation is that the galactic magnetic field significantly influences the expansion. We compare the properties of the ‘Crab-like’ remnants with those of the more common shell remnants and suggest that their essential differences are determined by the supernova outburst and not by the environment.