TITLE: GCN CIRCULAR NUMBER: 7593 SUBJECT: GRB 080413: ROTSE-III Detection of Optical Counterpart DATE: 08/04/13 03:03:03 GMT FROM: Wiphu Rujopakarn at U AZ/Steward GRB 080413: ROTSE-III Detection of Optical Counterpart E.S. Rykoff (UCSB), W. Rujopakarn (Steward), report on behalf of the ROTSE collaboration: ROTSE-IIIc, located at the H.E.S.S. site at Mt. Gamsberg, Namibia, responded to GRB 080413A (Swift trigger 309096). The first image was at 02:54:39.7 UT, 20.4 s after the burst (6.7 s after the GCN notice time). The unfiltered images are calibrated relative to USNO A2.0. We detect a 12.8 magnitude, fading source with coordinates: 19:09:11.8 -27:40:41.6 (J2000), with positional uncertainty of 1' or better start UT mag mlim(of image) ---------------------------------- 02:54:39.7 12.8 15.3 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/gsb309096_3c00_img.jpg Note that the object marked 7 is the candidate in question. Continuing observations are in progress.