Discovery of the Optical Counterpart of the Soft X-Ray Transient GRO:J0422+32

We report the discovery of the optical counterpart of the type II Soft X-ray Transient. GRO J0422+32 on 1992 August 15. ten days after the outburst. as well as the optical light curve during the first 100 days after the outburst, making GRO J0422+32 the slowest one in the optical decline. Archival plates searches show that the object did not undergo a similar outburst after 1928.

Its optical and X-ray evolution is similar to other members of its class. like V616 Mon. V404 Cyg and GRS 1124-68. For these later three there are dynamical evidences that place them among the best black holes candidates so far. These similarities suggest that the compact object in GRO J0422+32 may also be a black hole.