TITLE: GCN CIRCULAR NUMBER: 9332 SUBJECT: GRB 090510: Swift/UVOT Detection of a Candidate Optical Afterglow DATE: 09/05/10 01:26:57 GMT FROM: Frank Marshall at GSFC F. E. Marshall (GSFC) and E. A. Hoversten (PSU) report on behalf of the Swift team: UVOT took a second finding chart exposure of 250 seconds with the U filter starting 309 seconds after the BAT trigger for GRB 090510 (Hoversten et al. GCN Circ. 9331). There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 22:14:12.54 = 333.55227 DEC(J2000) = -26:34:58.4 = -26.58290 with a 90%-confidence error radius of about 0.69 arc sec. This position is 0.7 arc sec. from the center of the XRT error circle. The estimated magnitude is 18.95 with a 1-sigma error of about 0.17. No information about variability is available at this time. No correction has been made for the expected extinction corresponding to E(B-V) of 0.02.