TITLE: GCN CIRCULAR NUMBER: 9938 SUBJECT: GRB 090926A: Swift/UVOT detection of an optical afterglow DATE: 09/09/27 02:10:34 GMT FROM: Caryl Gronwall at PSU/Swift-UVOT C. Gronwall (PSU) and L. Vetere (PSU) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 090926A approximately 13 hours after the Fermi/GBM trigger (Bissaldi, GCN Circ. 9933). In a 357 sec observation in the white filter, we find a candidate optical afterglow within the XRT error circle (Vetere et al., GCN Circ. 9936) at RA(J2000) = 23:33:36.037 = 353.400154 Dec(J2000) = -66:19:26.64 = 66.324067 with a 90%-confidence error radius of about 0.11 arc sec. This position is 0.99 arc sec. from the center of the XRT error circle and is consistent with the optical afterglow position found by Skynet/PROMPT (Haislip et al., GCN Circ. 9937). The estimated magnitude is 18.78 +/- 0.04. This value is not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.03 in the direction of the burst (Schlegel et al. 1998).