TITLE: GCN CIRCULAR NUMBER: 6359 SUBJECT: GRB 070429B: ROTSE-III Optical Limits DATE: 07/04/29 03:56:35 GMT FROM: Brad Schaefer at LSU B. E. Schaefer (Louisiana State), W. Rujopakarn (U Mich), E.S. Rykoff (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 the short-burst GRB 070429B (Swift trigger 277582; Markwardt et al. GCN 6358), producing images beginning 7.9 s after the GCN notice time. An automated response took the first image at 03:09:30.9 UT, 26.5 s after the burst, under excellent conditions. We took 10 5-sec, 10 20-sec 20 60-sec exposures, and observations are continuing. 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 BAT error circle and within the error circle for the possible XRT source, for both single images and coadding into sets of 10; the field is not crowded. Individual images have limiting magnitudes ranging from 15.5-17.5; we set the following specific limits. start UT end UT t_exp(s) mlim t_start-tGRB(s) Coadd? -------------------------------------------------------------------- 03:09:30.9 03:09:35.9 5 15.5 26.5 N 03:09:30.8 03:10:56.5 85 17.3 26.4 Y 03:27:43.5 03:39:11.4 687 18.5 1119.1 Y