TITLE: GCN CIRCULAR NUMBER: 11551 SUBJECT: GRB 110107A: Swift/UVOT upper limits DATE: 11/01/10 19:20:46 GMT FROM: Stefan Immler at NASA/GSFC S. Immler (CRESST/UMCP/GSFC) and G. Stratta (ASDC) report on behalf of the Swift/UVOT team: Swift UVOT started observing the field of GRB 110107A on January 8, 2011 at 15:12 UT, approximately T+17.9 hours (Cummings, GCN Circ 11545). No optical afterglow consistent with the XRT position (Stratta et al., GCN Circ. 11547) is detected in individual or merged UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Poole et al. 2008, MNRAS, 383, 627) are: Filter T_start T_stop Exp(s) Mag ----------------------------------------------- v 64,646 75,090 2247 >20.5 u 64,609 74,538 1638 >21.2 ----------------------------------------------- The quoted upper limits have not been corrected for the expected Galactic extinction along the line of sight corresponding to a reddening of E_{B-V} = 0.459 mag (Schlegel et al., 1998, ApJS, 500, 525).