TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3322 SUBJECT: GRB 050502: ROTSE-III Detection of Possible Counterpart DATE: 05/05/02 02:55:44 GMT FROM: Sarah Yost at U.Michigan S.A. Yost, H. Swan (U Mich), B. A. Schaefer (Louisiana State), K. Alatalo (U Mich) report on behalf of the ROTSE collaboration: ROTSE-IIIb, located at McDonald Observatory, Texas, responsed to GRB 050502 (Integral trigger 2484) 23.3 s after the burst (5.0s after the GCN notice time), in conditions of variable clouds across the field. The unfiltered images are calibrated relative to USNO A2.0. Despite the changes in limiting magnitude due to the clouds, we see a 14.3rd magnitude, definitely fading source at: 13:29:46.3 +42:40:27.7 (J2000) The source is not visible in DSS (2nd epoch), 2MASS, or the MPChecker database. It is at ~14.3 mag, around 23.3 s after the burst in an image with a limiting magnitude of approximately 14.9. It is presently at ~ 18.5th mag, ~ 1000 sec post-burst. Continuing observations are in progress.