TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5504 SUBJECT: GRB 060904B: ROTSE-III Detection of Optical Counterpart DATE: 06/09/04 02:45:01 GMT FROM: Eli Rykoff at U of Michigan/ROTSE E.S. Rykoff (U Mich), W. Rujopakarn (U Mich), F. Yuan (U Mich), report on behalf of the ROTSE collaboration: ROTSE-IIIc, located at the H.E.S.S. site at Mt. Gamsberg, Namibia, responded to GRB 060904B (Swift trigger 228006). The first image was at 02:31:22.4 UT, 18.5 s after the burst (5.3 s after the GCN notice time). The unfiltered images are calibrated relative to USNO A2.0. We detect a 17.3 magnitude, brightening source with coordinates: 03:52:50.52 -00:43:30.85 (J2000) start UT mag mlim(of image) ---------------------------------- 02:31:22.4 17.3 18.1 A jpeg image is available at http://www.rotse.net/images/gsb228006_3c011-020_key.jpg Continuing observations are in progress. [GCN OPS NOTE(04sep06): Per author's request the 060904A was changed to B.]