TITLE: GCN CIRCULAR NUMBER: 23545 SUBJECT: GRB 181213A: Swift/UVOT Observations DATE: 18/12/18 20:20:49 GMT FROM: Mike Siegel at PSU/Swift MOC M. H. Siegel (PSU) and P. A. Evans (U. Leicester) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 181213A 2352 s after the BAT trigger (Evans et al., GCN Circ. 23525). A fading optical afterglow consistent with initial reports (Lipunov et al., GCN Circ. 23526, Hu et al., GCN Circ. 23529) was detected in four of UVOT���s filters. The lack of detection of this bright burst in the bluer filters would imply a redshift of z > 1.4, which is not inconsistent with the spectroscopic redshift of z < 2.4 from Heintz et al. (GCN Circ. 23537). The preliminary UVOT position is: RA (J2000) = 16:33:04.86 = 248.27025 (deg.) Dec (J2000) = +78:29:48.7 = 78.49685 (deg.) with an estimated uncertainty of 0.43 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) 2353 2503 294 17.33+/-0.04 white 2633 2653 19 17.15+/-0.10 white 8535 9061 513 19.03+/-0.07 white 66263 67021 738 >21.71 v 2683 2703 19 >17.35 v 26217 37929 1168 >20.45 b 2608 3393 87 17.82+/-0.10 b 8330 15947 230 19.18+/-0.23 b 65351 82801 1115 >20.39 u 2584 3318 216 17.25+/-0.06 u 14999 33141 1327 19.69+/-0.10 u 71983 72421 426 >20.32 uvw1 2559 3113 216 17.50+/-0.11 uvw1 14093 32991 2656 20.07+/-0.16 uvw1 71077 71977 885 >19.97 uvm2 2708 2908 196 >19.26 uvm2 19555 32084 2047 >20.84 uvw2 2659 2679 19 >17.50 uvw2 25310 37634 1771 >20.67 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).