A prompt radio burst from supernova 1987A in the Large Magellanic Cloud

Abstract

Supernova 1987A in the Large Magellanic Cloud was discovered1 on 24 February 1987; optical observations define the geocentric time of the explosion to be between February 23.10 and February 23.443 UT2,3. The supernova rose quickly to a visual magnitude of about 4.2 and has remained near that level since. Optical spectral line observations4 show that the photosphere was initially expand-ing at ∼16,000 km s−1 and that the supernova is probably of Type II, that is, from a massive progenitor star. Its position is coincident with a 12th magnitude blue star5 but International Ultraviolet Explorer (IUE) observations6 suggest that this blue star may still be present. The supernova progenitor star may therefore have been a fainter companion to this star. Radio emission from the supernova was detected at Australian observatories within two days of the increase in optical brightness. Here we report information obtained at four frequencies, namely 0.843, 1.415, 2.29 and 8.41 GHz. At frequencies around 1 GHz the peak flux density was about 150 mJy and occurred within four days of the supernova. The event may be a small precursor to a major flare of the type previously observed in radio supernova.