TITLE: GCN CIRCULAR NUMBER: 20190 SUBJECT: GRB 161117A: Swift/UVOT Detection DATE: 16/11/17 23:04:40 GMT FROM: Frank Marshall at GSFC F. E. Marshall (NASA/GSFC) and J. R. Cummings (NASA/UMBC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 161117A 69 s after the BAT trigger (Cummings et al., GCN Circ. 20179). A source consistent with the XRT position (Goad et al., GCN Circ. 20184) is detected in the initial UVOT exposures. The preliminary UVOT position is: RA (J2000) = 21:28:12.55 = 322.05230 (deg.) Dec (J2000) = -29:36:49.1 = -29.61365 (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 in the table below. The lack of detections in the m2 and w2 filters is consistent with the redshift of 1.549 reported by Malesani et al. (GCN Circ. 20180). Filter T_start(s) T_stop(s) Exp(s) Mag white 69 219 147 18.26 +/- 0.05 v 611 6146 255 18.77 +/- 0.19 b 536 5531 236 19.42 +/- 0.17 u 281 531 246 19.48 +/- 0.20 w1 660 6556 255 19.48 +/- 0.25 m2 1064 13173 712 >20.2 w2 586 11751 1141 >20.8 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.06 in the direction of the burst (Schlegel et al. 1998).