Discovery and early X-ray lightcurve of the transient GRS 1124-68 (Nova MUSCAE 1991).

The X-ray transient GRS 1124-68 was discovered by the all-sky X-ray monitor Watch onboard the Soviet satellite GRANAT on January 8A 1991. The 6-15 keV intensity was observed to increase from Jan 8 to Jan 13 reaching a peak flux of 2.2 Crab. Thereafter, the intensity declined reaching a minimum level on Jan 18. A second outburst was observed on Jan 24. A position derived from the Watch data initiated a search which lead eventually to the discovery of the optical counterpart on Jan 13. In spite of the similarity of this outburst to previous X-ray novae such as A 0620-00, further observations will be necessary to determine whether the compact object associated with GRS 1124-68 is a neutron star or a black hole.