SHELL-LIKE STRUCTURE IN 41.9+58, A POWERFUL SUPERNOVA REMNANT IN M82

An EVN map of the compact radio source 41.9 + 58 in M82 reveals a distorted shelllike structure with dimensions 0.56 × 0.32 pc. This map, together with a limit on the present expansion velocity (< 6500 kms-1 along the major axis) and the steady decay of the flux density (8.5 per cent yr-1 for the past 25 yr), convinces us that 41.9 + 58 is a powerful supernova remnant whose progenitor probably exploded 40-50 yr ago. Along with other examples, 41.9 + 58 has exhibited a radio luminosity 50-100 times greater than normal for remnants associated with optical type II supernovae and we suggest that such objects be classified as 'radio hypernova remnants'. © Royal Astronomical Society.