TITLE: GCN CIRCULAR NUMBER: 18881 SUBJECT: GRB 160117B: Swift/UVOT Detection DATE: 16/01/17 21:23:02 GMT FROM: Lea Hagen at PSU L. M. Z. Hagen (PSU) and E. Sonbas (Adiyaman Univ.) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 160117B 64 s after the BAT trigger (Sonbas et al. GCN Circ. 18875). We detect a fading source consistent with the XRT position (Evans et al. GCN Circ. 18880) and optical detections (Yurkov et al. GCN Circ. 18877, Kruehler et al. GCN Circ. 18878). The preliminary UVOT position is: RA (J2000) = 08:48:46.76 = 132.19485 (deg.) Dec (J2000) = -16:22:00.1 = -16.36670 (deg.) with an estimated uncertainty of 0.44 arc sec. (radius, 90% confidence). Preliminary detections 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 63 213 147 18.24+-0.06 white 876 1025 147 18.26+-0.06 white 5700 5899 196 19.22+-0.09 white 7136 7335 196 19.48+-0.11 v 6111 6311 196 >19.27 b 5495 5695 196 19.84+-0.26 b 6931 7131 196 >20.22 u 275 525 245 17.84+-0.08 u 5290 5489 196 19.13+-0.20 u 6725 6925 196 19.14+-0.21 w1 5085 5285 196 18.75+-0.19 w1 6521 6721 196 18.90+-0.21 m2 6316 6515 196 19.22+-0.29 w2 5905 6105 196 19.18+-0.23 w2 7341 7533 188 19.50+-0.31 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.07 in the direction of the burst (Schlegel et al. 1998).