TITLE: GCN CIRCULAR NUMBER: 6495 SUBJECT: GRB 070611: ROTSE-III Optical Limits DATE: 07/06/11 02:31:23 GMT FROM: Brad Schaefer at LSU Bradley E. Schaefer (Louisiana State), S.A. Yost (U Mich), E.S. Rykoff (U Mich), and 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 070611 (Swift trigger 282003; M. C. Stroh et al. 2007, GCN 6494), producing images beginning 7.6 s after the GCN notice time. An automated response took the first image at 01:57:58.6 UT, 44.7 s after the burst, under excellent conditions. We took 10 5-sec, 10 20-sec and 20 60-sec exposures, with further exposures now ongoing. These unfiltered images are calibrated relative to USNO A2.0 (R). Comparison to the DSS (second epoch) reveals no new sources within the 3-sigma Swift/BAT error circle; the field is not crowded. Individual images have limiting magnitudes ranging from 15.7-17.2; we set the following specific limits. start UT end UT t_exp(s) mlim t_start-tGRB(s) Coadd? -------------------------------------------------------------------- 01:57:58.6 01:58:03.6 5 15.8 44.7 N 01:57:58.6 01:59:16.6 78 17.0 44.7 Y 02:04:20.5 02:15:45.2 684 18.3 426.6 Y