TITLE: GCN CIRCULAR NUMBER: 10119 SUBJECT: GRB 091102: ROTSE-III Optical Limits DATE: 09/11/02 15:34:52 GMT FROM: Brad Schaefer at LSU B. E. Schaefer (Louisiana State), F. Yuan (U Mich), S. B. Pandey (U Mich), report on behalf of the ROTSE collaboration: ROTSE-IIIa, located at Siding Spring Observatory, Australia, responded to GRB 091102 (Swift trigger 374598; Hoversten et al., GCN 10117), producing images beginning 5.8 s after the GCN notice time. An automated response took the first image at 14:35:04.8 UT, 26.5 s after the burst, under fair conditions with occassional thin clouds and a bright Full Moon 96 degrees away. We took 10 5-sec, 10 20-sec and 100 60-sec exposures. These unfiltered images are calibrated relative to USNO A2.0 (R). Imaging is on going. Comparison to the DSS (second epoch) reveals no new sources within the 3-sigma Swift/BAT error circle, for both single images and coadding into sets of 10. No XRT position is available. Individual images have limiting magnitudes ranging from 13.7-16.0; we set the following specific limits. start UT end UT t_exp(s) mlim t_start-tGRB(s) Coadd? -------------------------------------------------------------------- 14:35:04.8 14:35:09.8 5 14.6 26.5 N 14:35:04.8 14:37:16.8 50 15.5 26.5 Y 14:37:25.9 14:42:08.0 282 16.6 167.6 Y