1994A&A...285..687A

Radio emission observed recently from SN1987A and from SN1978K, an unusual supernova in NGC 1313, is probably the result of synchrotron emission from electrons accelerated by the expanding supernova shocks. Both these supernovae are believed to involve progenitors with a history of significant mass loss, and so the magnetic field into which the supernova shock is expanding is likely to be a tightly-wound spiral. After switching on in the radio for the second time in June 1990, the radio flux from supernova 1987A has increased more or less steadily for the last 2 1/2 years. Some fourteen years after explosion SN1978K is a very strong X-ray and radio source and the emission is probably associated with a strong shock propagating into the unusually dense wind of the progenitor star. We consider the requirements for efficient particle acceleration in such sources, given that the `shock-magnetic field' geometry is likely to be quasi-perpendicular, and the shock is almost certainly sweeping along magnetic field lines at speeds in excess of the speed of light. We address the two most likely mechanisms for the cross-field transport required for efficient acceleration at superluminal quasi-perpendicular shocks-resonant scattering by MHD waves and magnetic field line wandering (or braiding). The results are applied to the observed radio emission from SN1978K and SN1987A, and the observed flux density is used to set limits on the relevant source parameters.