TITLE: GCN CIRCULAR NUMBER: 23138 SUBJECT: GRB 180812A: Swift/UVOT Detection DATE: 18/08/13 18:24:45 GMT FROM: Sam LaPorte at PSU GRB 180812A: Swift/UVOT Detection S. J. LaPorte (PSU) and A. Y. Lien (GSFC/UMBC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 180812A 112 s after the BAT trigger (Lien et al., GCN Circ. 23129). A fading source consistent with the XRT position (Goad et al. GCN Circ. 23131) is detected in the initial UVOT exposures. The preliminary UVOT position is: RA (J2000) = 16:23:20.45 = 245.83522 (deg.) Dec (J2000) = 74:39:52.9 = 74.66471 (deg.) with an estimated uncertainty of 0.50 arc sec. (radius, 90% confidence), consistent with detections reported by BOOTES-5/JGT (Carrasco et al. GCN Circ. 23130) and COATLI (Watson et al. GCN Circ. 23132). Preliminary detections and 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white 140 289 431 19.81 +/- 0.17 white 1551 2092 77 >20.85 v 600 6610 372 >18.9 b 526 5994 352 >20.0 u 270 5789 598 >19.8 w1 650 6857 211 >19.5 m2 6616 6815 197 >20.2 w2 6206 6406 197 >20.2 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.04 in the direction of the burst (Schlegel et al. 1998).