TITLE: GCN CIRCULAR NUMBER: 11264 SUBJECT: GRB 100909A: ROTSE-III Optical Limits DATE: 10/09/09 14:29:13 GMT FROM: Brad Schaefer at LSU B. E. Schaefer (Louisiana State) reports on behalf of the ROTSE collaboration: ROTSE-IIIb, located at McDonald Observatory, Texas, responded to GRB 100909A (INTEGRAL trigger 6060; Mereghetti et al., GCN 11260), producing images beginning 6.4 s after the GCN notice time. An automated response took the first image at 10:41:45.5 UT, 5811.6 s after the burst. For the first 20 minutes the conditions were partly cloudy with occassional holes, but after 11:02 UT the sky became clear and excellent. We took 10 5-sec, 10 20-sec and 116 60-sec exposures. 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 INTEGRAL/IBIS error circle, for both single images and coadding into sets of 10. The Swift XRT team reports that a faint X-ray source is visible at 12:19 UT (Siegel et al. 2010, GCN 11261), and we have also closely examined this error circle, again finding no variable star or object of interest. The Swift XRT position is not crowded, although there is one fairly faint star in it. Individual images have limiting magnitudes ranging from 12.8-17.6; we set the following specific limits. start UT end UT t_exp(s) mlim t_start-tGRB(s) Coadd? -------------------------------------------------------------------- 10:44:07.5 10:45:25.7 78 15.7 5953.6 Y 11:02:58.7 11:07:40.0 281 18.5 7084.8 Y