About three years after the initial burst,
radio emission was
again detected from SN1987A, first at Molonglo and then a few weeks later at
the Australia Telescope Compact Array (ATCA). Since then, the flux density has
climbed, initially rapidly and then since about 1996, almost exponentially
with time constant about 2500 days at all frequencies (Zanardo et al. 2010, ApJ, 710, 1515).
This emission originates from shock acceleration of electrons by interaction
of the expanding ejecta with the circumstellar gas and signals the birth of a
radio supernova remnant.