TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4121 SUBJECT: GRB 051021: ROTSE-III Confirmation of Optical Counterpart DATE: 05/10/21 17:37:42 GMT FROM: Heather Swan at U.of Michigan/ROTSE H. Swan (U Mich), T.A. McKay (U Mich), D.A. Smith (Guilford), B. Schaefer (Louisiana State), E.S. Rykoff (U Mich), F. Yuan (U Mich), report on behalf of the ROTSE collaboration: ROTSE-IIIa, located at Siding Spring Observatory, Australia, responded to GRB 051021 (HETE trigger 3947). The first image was at 13:22:28.4 UT, 31.8 s after the burst (6.6 s after the GCN notice time). The unfiltered images are calibrated relative to USNO A2.0. We confirm the presence of the source detected by Fox et. al. GCN # 4120. We observe the source to rise to 16.9 magnitude, at about 180 seconds, and then fade by half a magnitude over a period of 150 seconds. This source is not visible in DSS (second epoch), 2MASS or the MPChecker database. Continuing observations are in progress. >