TITLE: GCN CIRCULAR NUMBER: 13745 SUBJECT: GRB 120911A: ROTSE-III Optical Limits DATE: 12/09/11 07:45:30 GMT FROM: Wiphu Rujopakarn at U AZ/Steward W. Rujopakarn (Steward), T. Guver (Sabanci U), report on behalf of the ROTSE collaboration: ROTSE-IIIb, located at McDonald Observatory, Texas, responded to GRB 120911A (Swift trigger 533268; Cannizzo et al., GCN 13744), producing images beginning 9.2 s after the GCN notice time. An automated response took the first image at 07:09:04.2 UT, 30.4 s after the burst, under fair conditions. We took 10 5-sec, 10 20-sec and 40 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; however, we are limited as the field is somewhat crowded. Individual images have limiting magnitudes ranging from 15.5-16.6; we set the following specific limits. start UT end UT t_exp(s) mlim t_start-tGRB(s) Coadd? -------------------------------------------------------------------- 07:09:04.2 07:09:09.2 5 15.5 30.4 N 07:09:04.2 07:10:46.4 50 16.9 30.4 Y