The development of the radio remnant of SN 1987A has been followed using the Australia Telescope Compact Array since its first detection in 1990 August. The remnant has been observed at four frequencies, 1.4, 2.4, 4.8, and 8.6 GHz, at intervals of 4–6 weeks since the first detection. These data are combined with the 843 MHz data set of Ball et al. (2001) obtained at Molonglo Observatory to study the spectral and temporal variations of the emission. These observations show that the remnant continues to increase in brightness, with a larger rate of increase at recent times. They also show that the radio spectrum is becoming flatter, with the spectral index changing from −0.97 to −0.88 over the 11 years. In addition, at roughly yearly intervals since 1992, the remnant has been imaged at 9 GHz using super-resolution techniques to obtain an effective synthesised beamwidth of about 0″.5. The imaging observations confirm the shell morphology of the radio remnant and show that it continues to expand at ˜3000 km s−1. The bright regions of radio emission seen on the limb of the shell do not appear to be related to the optical hot spots which have subsequently appeared in surrounding circumstellar material.

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SummarySN1987A has an intrinsic radio luminosity some four orders of magnitude less than SN1993J at maximum, largely a reflection of the tenuous wind . from the progenitor of SN1987A before explosion. Both remnants have an edge-brightened, ring-like morphology though, in the case of SN1987A, the expansion rate is currently only around 3500 km s−1. The flux density of the remnant of SN1987A continues to rise at all measured radio frequencies. Its spectral index is gradually flattening, indicating its transition into the supernova remnant phase. A campaign to increase the resolution of radio imaging by observing at higher frequencies is underway with the Australia Telescope Compact Array (ATCA).

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