TITLE: GCN CIRCULAR NUMBER: 13973 SUBJECT: GRB 121117A: Swift/UVOT Observations DATE: 12/11/18 12:41:31 GMT FROM: Samantha Oates at MSSL S. R. Oates (MSSL-UCL) 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 121117A s after the BAT trigger (Cummings et al., GCN Circ. 13967). We find an optical afterglow consistent with the XRT position (Beardmore et al. GCN Circ. 13972) in the initial UVOT white exposure. The refined UVOT position is (RA,DEC) = 31.61063, 7.41956 (J2000), which is equivalent to: RA (J2000) = 02:06:26.56 Dec (J2000) = +07:25:10.5 with an estimated uncertainty of 0.6 arcsec (radius, 90% confidence). Preliminary magnitudes and 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the initial exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white (FC) 57 205 146 19.17 +/- 0.10 white 4606 10267 1150 >21.9 v 3580 11882 1077 >20.3 b 4400 6037 393 >20.6 u 4195 5831 393 >20.3 w1 3990 5627 393 >20.3 m2 3785 5421 393 >20.2 w2 4811 11174 1082 >21.3 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).