TITLE: GCN CIRCULAR NUMBER: 9102 SUBJECT: GRB 090407: ROTSE-III Optical Limits DATE: 09/04/07 11:06:47 GMT FROM: Brad Schaefer at LSU B. E. Schaefer (Louisiana State), F. Yuan (U Mich), report on behalf of the ROTSE collaboration: ROTSE-IIIa, located at Siding Spring Observatory, Australia, responded to GRB 090407 (Swift trigger 348650; H. Ziaeepour et al., GCN 9101), producing images beginning 8.8 s after the GCN notice time. An automated response took the first image at 10:29:05.8 UT, 40.2 s after the burst, and during the gamma-ray emission, under fair conditions. We took 10 5-sec, 10 20-sec and 33 60-sec exposures. These unfiltered images are calibrated relative to USNO A2.0 (R). Imaging is on going but the source is getting low. Comparison to the DSS (second epoch) reveals no new sources within the 3-sigma Swift/BAT error circle or the XRT error circle, for both single images and coadding into sets of 10; the field is not crowded. Individual images have limiting magnitudes ranging from 13.9-15.5; we set the following specific limits. start UT end UT t_exp(s) mlim t_start-tGRB(s) Coadd? -------------------------------------------------------------------- 10:29:05.8 10:29:10.8 5 14.1 40.2 N 10:29:05.8 10:31:19.0 133 16.1 40.2 Y