TITLE: GCN CIRCULAR NUMBER: 6269 SUBJECT: GRB 070411: ROTSE-III Detection of Optical Counterpart DATE: 07/04/11 21:21:03 GMT FROM: Eli Rykoff at U of Michigan/ROTSE E.S. Rykoff (U Mich), W. Rujopakarn (Steward), R. Quimby (U Texas), B. E. Schaefer (Louisiana State), H. Swan (U Mich), S.A. Yost (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 070411 (Swift trigger 275087, GCN 6267, Moretti, et al.). The first image was at 20:15:25.1 UT, 172 s after the burst; the response was delayed due to a GCN connection problem. We took 10 5s exposures followed by 50+ 20s exposures. The unfiltered images are calibrated relative to USNO B1.0, and no correction has been made for the large Galactic extinction in the direction of the burst. We confirm the afterglow candidate reported by Moretti, et al. (GCN 6267) and Kann, et al. (GCN 6268). The afterglow was marginally detected in the first few coadded images (stacking 10 images at a time). We see the afterglow brighten significantly during our observations, to a peak of 17.7+/-0.1 mag, around 900s after the burst; due to the faint afterglow, our time resolution is very coarse. start UT exptime tstart-tburst (s) mag ---------------------------------------------------------- 20:15:25.2 50.0 172 18.2+/-0.4 20:21:53.7 200.0 560 18.5+/-0.4 20:26:50.0 200.0 856 17.7+/-0.1 20:31:45.8 200.0 1152 18.6+/-0.4 A jpeg image is available at http://www.rotse.net/images/gsb275087_3c031-040_key.jpg Continuing observations are in progress.