A major problem in the study of Crablike supernova remnants concerns the nature of their interaction with an external medium. The authors report new radio observations made with the Very Large Array (VLA) searching for radio emission outside the Crablike remnant 3C 58, where the supernova ejecta might be expected to be interacting with the interstellar medium. They have failed to find evidence for any such emission. However, the authors review the morphological and spectral evidence for such interaction and conclude that a normal, steep-spectrum, limb-brightened shell is not an appreciable component of the observed emission. If 3C 58 resulted from a normal Type II supernova, either its shock is unusually inefficient at producing relativistic particles and magnetic field, or the ambient density is very low. If there is no outer blast wave, standard ideas about Crablike remnants need serious revision.
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Reynolds et al. (1985) studied this question.