TITLE: GCN CIRCULAR NUMBER: 9946 SUBJECT: GRB 090927: Swift/UVOT detection of an optical afterglow DATE: 09/09/27 10:58:19 GMT FROM: Caryl Gronwall at PSU/Swift-UVOT C. Gronwall and D. Grupe (PSU) report on behalf of the Swift/UVOT team: In response to GRB090927 (Swift/BAT trigger 370846) at 10:07:16 UT, UVOT took a finding chart exposure of 150 seconds with the White filter starting 2141 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 22:55:53.41 = 343.97255 DEC(J2000) = -70:58:49.3 = -70.98037 with a 90%-confidence error radius of about 0.63 arc sec. This position is 7.2 arc sec. from the center of the XRT error circle. The estimated magnitude is 19.10 with a 1-sigma error of about 0.15. No correction has been made for the expected extinction corresponding to E(B-V) of 0.03.