TITLE: GCN CIRCULAR NUMBER: 13050 SUBJECT: GRB 120311B: C88 optical limits DATE: 12/03/12 18:32:49 GMT FROM: Simone Leonini at Monarrenti Obs Simone Leonini and Paolo Rosi (Montarrenti Observatory, Siena, Italy) report: We observed the field of GRB 120311B (Swift trigger 517489, Marshall et al., GCN Circ 13038) with 0.53m RC telescope + U47 detector at Montarrenti Observatory (Siena, Italy, IAU code C88). The first session of observations was started at 2012-03-12 03:59:24 UT and stopped at 2012-03-12 04:00:07 UT. The second session started at 04:11:47 UT and stopped at 04.12.26 UT (~13 hours after the trigger). Four unfiltered images of 40s exposure was obtained. We do not detect any new point source in the coadded images (limit R~18.9, USNO-B1 catalogue) within the enhanced XRT error circle (Osborne et al., GCN Circ. 13042). Target was very low on the horizon. [GCN OPS NOTE(12mar12): Distribution was delayed by ~3 hrs until an account could be created.]