... Australia Telescope Steering Committee . ... Parkes radio telescope . ... Such a model can reproduce much of the observed late-time evolution of the radio flux density and spectral index (though recent results for SNб 1993J (van Dyk et al. 1994) show that the Chevalier model does not adequately describe the early behaviour of radio light curves for this supernova, perhaps due to variations in the mass-loss rate and clumping in the stellar wind, which are not yet accounted for in the model). ...