  Supernova 1987A in the Large Magellanic Cloud provides a spectacularly
detailed view of the aftermath of a core-collapse explosion. The supernova
ejecta initially coasted outward at more than 10% of the speed of light, but in
1990 were observed to decelerate rapidly as they began to encounter dense
circumstellar material expelled by the progenitor star. The resulting shock has
subsequently produced steadily brightening radio synchrotron emission, which is
resolved by the Australia Telescope Compact Array (ATCA) into an expanding
limb-brightened shell. Here we present 15 years of ATCA imaging of Supernova
1987A, at an effective angular resolution of 0.4 arcsec. We find that the radio
remnant has accelerated in its expansion over this period, from approx 3600
km/s in 1992 to approx 5200 km/s at the end of 2006. The published diameters of
the evolving X-ray shell have been ~15% smaller than the corresponding radio
values, but a simultaneous Fourier analysis of both radio and X-ray data
eliminates this discrepancy, and yields a current diameter for the shell in
both wave-bands of approx 1.7 arcsec. An asymmetric brightness distribution is
seen in radio images at all ATCA epochs: the eastern and western rims have
higher fluxes than the northern and southern regions, indicating that most of
the radio emission comes from the equatorial plane of the system, where the
progenitor star's circumstellar wind is thought to be densest. The eastern lobe
is brighter than and further from the supernova site than the western lobe,
suggesting an additional asymmetry in the initial distribution of supernova
ejecta.
