TITLE: GCN CIRCULAR NUMBER: 11816 SUBJECT: GRB 110318B: Swift/UVOT Upper Limits DATE: 11/03/21 14:53:29 GMT FROM: Stephen Holland at USRA/NASA/GSFC/SSC S. T. Holland (CRESST/USRA/GSFC) and R. Margutti (INAF-OAB) report on behalf of the Swift/UVOT team: The Swift/UVOT observed the field of GRB 110318B starting 58 s after the BAT trigger (Margutti, et al., 2011, GCN Circ. 11799). Settled observations started at 76 s. We do not detect an optical afterglow at the UVOT-enhanced XRT position (Evans, et al., 2011, GCN Circ. 11803) in any of the UVOT filters. Preliminary 3-sigma upper limits for detecting a source in the finding charts and in the co-added images, are Filter T_start T_stop Exp(s) Mag ----------------------------------------------- white (fc) 76 226 147 >21.5 868 1018 147 >21.5 v 619 7035 529 >20.6 b 545 7693 370 >21.2 u 289 7649 756 >21.2 uvw1 668 7445 529 >20.8 uvm2 5602 7239 393 >20.5 uvw2 1024 6829 236 >20.3 white 76 6623 626 >22.2 ----------------------------------------------- The quoted magnitudes and upper limits have not been corrected for the expected Galactic extinction along the line of sight corresponding to a reddening of E_{B-V} = 0.46 mag (Schlegel, et al., 1998, ApJS, 500, 525).