PARTICLE-ACCELERATION AT SUPERLUMINAL QUASI-PERPENDICULAR SHOCKS - APPLICATION TO SN1978K AND SN1987A

Radio emission observed recently from SN1987A and from SN1978K, an unu sual supernova in NGC 1313, is probably the result of synchrotron emis sion from electrons accelerated by the expanding supernova shocks. Bot h these supernovae are believed to involve progenitors with a history of significant mass loss, and so the magnetic field into which the sup ernova shock is expanding is likely to be a tightly-wound spiral. Afte r switching on in the radio for the second time in June 1990, the radi o flux from supernova 1987A has increased more or less steadily for th e last 2 1/2 years. Some fourteen years after explosion SN1978K is a v ery strong X-ray and radio source and the emission is probably associa ted with a strong shock propagating into the unusually dense wind of t he progenitor star. We consider the requirements for efficient particl e acceleration in such sources, given that the 'shock - magnetic field ' geometry is likely to be quasi-perpendicular, and the shock is almos t 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 superlum inal 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 obser ved flux density is used to set limits on the relevant source paramete rs.