TITLE: GCN CIRCULAR NUMBER: 6734 SUBJECT: GRB 070810: ROTSE-III Detection of Optical Counterpart DATE: 07/08/10 03:12:03 GMT FROM: Heather Swan at U.of Michigan/ROTSE H. Swan (U Mich), B. E. Schaefer (Louisiana State), E.S. Rykoff (U Mich), report on behalf of the ROTSE collaboration: ROTSE-IIIb, located at McDonald Observatory, Texas, responded to GRB 070810 (Swift trigger 287364). The first image was at 02:34:02.5 UT, 1330.5 s after the burst. The unfiltered images are calibrated relative to USNO A2.0. We detect a 16.7 magnitude, fading source with coordinates: 12:39:51.48 +10:45:00.90 (J2000). The source is blended with a nearby USNO star visible in the DSS, and thus our initial positional uncertainty is ~3". start UT mag mlim(of image) ---------------------------------- 02:29:53.4 16.7 18.5 This source is not visible in DSS (second epoch), 2MASS or the MPChecker database. A jpeg image is available at http://www.rotse.net/images/gsb0174_3b01_img.jpg Continuing observations are in progress.