TITLE: GCN CIRCULAR NUMBER: 29177 SUBJECT: GRB 201223A: Swift/UVOT Detection DATE: 20/12/26 22:03:09 GMT FROM: Alexander Belles at PSU/Swift ​A. Belles (PSU) and J. D. Gropp (PSU) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 201223A 79 s after the BAT trigger (Gropp et al., GCN Circ. 29158). A source consistent with the XRT position (Goad et al., GCN Circ. 29170) is detected in the initial UVOT exposures. The preliminary UVOT position is: RA (J2000) = 08:51:09.51 = 132.78961 (deg.) Dec (J2000) = +71:10:47.4 = 71.17984 (deg.) with an estimated uncertainty of 0.42 arc sec. (radius, 90% confidence). 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_FC 79 229 147 16.06+/-0.03 white 571 1019 186 18.04+/-0.08 white 5921 6121 196 >20.17 white 12121 12630 497 20.09+/-0.30 v 621 1069 58 >17.44 b 547 1167 58 17.97+/-0.25 b 11208 12115 885 >20.38 u_FC 292 541 246 16.75 +/- 0.04 u 694 1142 38 >17.58 w1 670 1118 58 >17.65 m2 645 1093 58 >17.87 w2 596 1045 58 >17.81 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).