TITLE: GCN CIRCULAR NUMBER: 14092 SUBJECT: GRB 121217A: Swift/UVOT Detection DATE: 12/12/17 18:14:46 GMT FROM: Samantha Oates at MSSL S. R. Oates (MSSL-UCL) and M. H. Siegel (PSU) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 121217A 73 s after the BAT trigger (Siegel et al., GCN Circ. 14089). A source consistent with the GROND optical position (Elliott et al. GCN Circ. 14091) is detected in the initial UVOT exposures. The preliminary UVOT position is: RA (J2000) = 10:14:50.32 = 153.7097 (deg) Dec (J2000) = -62:21:03.3 = -62.35096 (deg) with an estimated uncertainty of 0.6 arcsec (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 73 222 147 19.58 +/- 0.13 v 616 5906 313 19.01 +/- 0.22 b 541 560 19 18.76 +/- 0.36 u 285 6522 540 20.09 +/- 0.34 w1 666 6317 313 >19.96 m2 641 6112 313 >19.85 w2 591 7138 510 >20.37 The magnitudes in the table are not corrected for the significant Galactic extinction due to the reddening of E(B-V) = 0.37 in the direction of the burst (Schlegel et al. 1998).