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-rav 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.