TITLE: GCN CIRCULAR NUMBER: 11334 SUBJECT: GRB 101011A: Swift/UVOT Observations of a Possible Optical Afterglow DATE: 10/10/11 23:16:27 GMT FROM: Stephen Holland at USRA/NASA/GSFC/SSC S. T. Holland (CRESST/GSFC/USRA) and M. De Pasquale (UCL-MSSL) report on the behalf of the Swift UVOT team: The Swift/UVOT observed the field of GRB 101011A starting 66 s after the BAT trigger (Cannizzo, et al., 2010, GCN Circ. 11331). Settled observations started at 85 s. We detect an optical source that may be fading and is not present in the USNO-B1.0 catalogue, 2MASS point source catalogue, or the DSS. The preliminary UVOT position is: RA (J2000) = 03:13:10.47 = 48.29363 (deg) Dec (J2000) = -65:58:54.7 = -65.98186 (deg) with an estimated uncertainty of 1.14 arcsec (radius, 90% confidence, statistical + systematic). This is 1.84 arcsec west of the UVOT-enhanced XRT position (Evans, et al., 2010, GCN Circ. 11333). Preliminary white magnitudes and 3-sigma upper limits for the source are: Filter T_start T_stop Exp(s) Mag Err ----------------------------------------------------------- white (fc) 85 235 147 21.38 0.34 white 876 1025 147 >21.7 ----------------------------------------------------------- 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} = 0.03 mag (Schlegel, et al., 1998, ApJS, 500, 525). All photometry is on the UVOT photometry system described in Poole et al. (2008, MNRAS, 383, 627).