BIRTH OF A RADIO SUPERNOVA REMNANT IN SUPERNOVA-1987A

FOLLOWING an initial radio outburst 1 which decayed on a timescale of a few weeks, supernova 1987A 2 was undetectable at radio wavelengths until recently. In mid-1990, 1,200 days after the explosion, radio emission was once again detected 3 with the Molonglo Observatory Synthesis Telescope and the Australia Telescope Compact Array. Our observations since then show that the source has increased in strength at all monitored frequencies between 843 MHz and 8.6 GHz, with considerable variations in spectral index. The extended radio emission is centred within 0.5 arcsec of the optical supernova, and probably lies within the [O III] ring imaged by the Hubble Space Telescope. We interpret the emission as optically thin synchrotron emission from shock-accelerated electrons. This is the first time the birth of a nearby radio supernova remnant has been witnessed, and future observations will allow the structure of the remnant to be compared with the many other known radio remnants.