Detection of possible optical flashes from the γ-ray burst source GBS0526–66

The unidentified source of the γ -ray burst of 5 March 1979, GBS0526–66, may be located in the supernova remnant N49 in the Large Magellanic Cloud 1 , though some authors 2,3 have questioned the implied distance of 55 kpc. Among several unusual features of the source (reviewed by Cline 4 ) is its repeatability: a total of 16 γ -ray bursts have been reported 3 , which may be periodic 5 . Only γ -ray bursts have been detected from this source. The situation for other γ -ray burst sources is not very different. Optical transients are known, in three cases 6,7 , to have occurred near positions of later γ -ray bursts. Even so, no source has been identified optically 8–10 , and only upper limits are known for simultanous emission of optical radiation with γ -ray bursts 11 . Here we report that GBS0526–66 was monitored for ∼910 h, using a high speed photoelectric photometer, attached to a 50 cm telescope at ESO/La Silla. Three short optical flashes were found, which may possibly be related to the γ -ray burst phenomenon. The most intense of these occurred on 1984 February 8 UT 07:42. It reached a maximum brightness corresponding to m (visual) = 8.7. The shape of the light curve bears remarkable similarity to the initial 200 ms of the 1979 March γ -ray burst.