TITLE: GCN CIRCULAR NUMBER: 20455 SUBJECT: GRB 170113A: Swift/UVOT Observations DATE: 17/01/13 20:40:06 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 170113A 68 s after the BAT trigger (Evans et al., GCN Circ. 20446). A fading source consistent with the XRT position (Goad et al. GCN Circ. 20450) is detected in the initial UVOT exposures. The preliminary UVOT position is: RA (J2000) = 04:06:55.86 = 61.73276 (deg.) Dec (J2000) = -71:56:34.9 = -71.94302 (deg.) with an estimated uncertainty of 0.44 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) 68 217 147 18.27+-0.06 white 560 1009 186 19.56+-0.11 white 1163 1875 97 19.65+-0.17 white 6392 6592 196 20.64+-0.26 v 609 1751 136 19.09+-0.36 v 5367 7002 393 >19.49 b 535 1850 136 19.33+-0.19 b 6188 6388 196 >20.39 u (fc) 280 530 245 18.76+-0.13 u 683 1825 116 19.33+-0.27 u 5983 7615 390 >20.44 uvw1 659 1801 136 >19.38 uvm2 634 1776 136 >19.12 uvw2 585 1727 136 >19.42 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.11 in the direction of the burst (Schlegel et al. 1998).