Constraints on the optical counterpart of GBS 0526-66.

Upper limits to the magnitude of the pulsed optical emission of the quiescent counterpart of GBS 0526-66 (the source of the March 5, 1979b gamma-ray burst) are derived from the survey of the N49 supernova remnant carried out at the 50 cm telescope at ESO, La Silla in 1983 and 1984. The possibility that part of the emission is modulated is discussed, leading to a lower limit to the magnitude of a periodic component of about 19.4. The results are discussed in the framework of present theoretical models of gamma-ray bursts.