TITLE: GCN CIRCULAR NUMBER: 9622 SUBJECT: GRB 090708: ROTSE-III Optical Limits DATE: 09/07/08 03:58:49 GMT FROM: Fang Yuan at ROTSE F. Yuan (U Mich), E.S. Rykoff (UCSB), H. Flewelling (IfA/Hawaii), T. Guver (U Arizona), S. B. Pandey (U Mich), W. Rujopakarn (Steward), report on behalf of the ROTSE collaboration: ROTSE-IIIb, located at McDonald Observatory, Texas, responded to GRB 090708 (Swift trigger 356776; Krimm et al., GCN 9621), producing images beginning 7.4 s after the GCN notice time. An automated response took the first image at 03:39:04.5 UT, 49.2 s after the burst, under fair conditions. We took 10 5-sec, 10 20-sec and 10 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. Individual images have limiting magnitudes ranging from 14.8-16.1; we set the following specific limits. start UT end UT t_exp(s) mlim t_start-tGRB(s) Coadd? -------------------------------------------------------------------- 03:39:04.5 03:39:09.5 5 15.0 49.2 N 03:39:04.5 03:40:11.6 67 16.6 49.2 Y 03:40:27.8 03:45:35.8 308 17.4 132.5 Y