RADIO-EMISSION FROM SNR 1987A

Diffusive acceleration of electrons by the blast wave of SNR 1987A is shown to provide a reasonable fit to observations of the radio emission since it reappeared in 1990 July. As well as determining the diffusion coefficient in this model, the observations indicate that the compression ratio of the gas subshock embedded in the blast wave is similar to 2.7, much lower than the value of 4 expected of a strong shock front. We propose that protons accelerated by the shock front itself cause the weakening of the subshock by both heating and accelerating the upstream plasma, producing a structure with a precursor to the gas subshock. Preliminary calculations using a fluid model for the energetic particle population indicate that these effects can significantly weaken the subshock just a few uears after the explosion, if the same rate of particle injection is assumed as in other models of the acceleration of cosmic rays.