TITLE: GCN CIRCULAR NUMBER: 8656 SUBJECT: GRB 081211: Swift/UVOT detection of an optical afterglow DATE: 08/12/11 21:33:35 GMT FROM: Stefan Immler at NASA/GSFC S. Immler (CRESST/UMD/GSFC), S. T. Holland (CRESST/USRA/GSFC), and H. A. Krimm (CRESST/GSFC/USRA) report on behalf of the Swift UVOT team: Further analysis of Swift Ultraviolet/Optical Telescope (UVOT) data of GRB 081211 (Krimm et al., GCN Circ. 8653), starting 113 sec after the BAT trigger, gives a detection of an optical source within the enhanced Swift-XRT position (Beardmore et al., GCN Circ. 8655) at RA (J2000) 21:52:27.97 = 328.11654 (deg) Dec (J2000) -33:50:08.3 = -33.83565 (deg) with an uncertainty of 0.7 arcseconds (radius, 90% containment) in the white filters at 4.5-sigma level of confidence. The source is not present in DSS, the USNO-B1.0 catalogue, or the 2MASS point source catalogue. It is not detected in any of the other UVOT filters at the limiting magnitudes reported below. Filter Tstart(s) Tstop(s) Exp(s) Magnitude wh 113 7134 588 21.23+/-0.39 u 326 6724 265 >20.23 (3-sigma UL) b 582 741 293 >20.24 (3-sigma UL) uvw2 632 7318 371 >20.40 (3-sigma UL) v 656 11966 386 >19.38 (3-sigma UL) uvm2 681 6314 136 >19.58 (3-sigma UL) uvw1 706 6519 196 >19.87 (3-sigma UL) The values quoted above are in the UVOT photometric system (Poole et al. 2008, MNRAS, 383, 627) and are not corrected for the expected Galactic extinction along the line of sight which corresponds to a reddening of E(B-V)=0.077 mag (Schlegel et al. 1998).