STRUCTURE IN THE RADIO REMNANT OF SUPERNOVA-1987A

The radio emission associated with SN 1987A appears to be synchrotron emission resulting from the acceleration of electrons at the interface between the outward moving shock wave and clumps of circumstellar mat erial. The Australia Telescope Compact Array is now able to resolve th is region, which has dimensions of approximately arcsec, revealing a s light (10%) asphericity in the distribution of the low density gas wit hin the [OIII] circumstellar ring. Assuming that the radio emission ar ises from a region just behind the shock front, we deduce a mean radia l expansion velocity, from 1987 to 1992, of 29 200 kms. First observed contact of the shock with the [OIII] circumstellar ring could occur a s early as mid- 1993, depending on the deceleration in the intervening gas. This will probably be closely followed by shock-excited optical lines, a strong X-ray outburst and a further increase in the radio emi ssion.