TITLE: GCN CIRCULAR NUMBER: 14017 SUBJECT: GRB 121128A: Swift/UVOT Detection DATE: 12/11/28 22:58:50 GMT FROM: Samantha Oates at MSSL S. R. Oates (MSSL-UCL) reports on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 121128A 85 s after the BAT trigger (Oates et al., GCN Circ. 14007). A source consistent with the XRT position (Osborne et al., GCN Circ. 14015) is detected in the initial white, v, b and u exposures only. The non-detection in the UV filters is consistent with the redshift of z=2.2 reported by Gemini North (Tanvir et al., GCN Circ. 14009) The preliminary UVOT position is: RA (J2000) = 20:02:24.00 = 300.60000 (deg.) Dec (J2000) = +54:17:59.1 = 54.29974 (deg.) with an estimated uncertainty of 0.50 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 85 235 147 16.19 +/- 0.03 v 629 649 19 17.00 +/- 0.23 b 554 573 20 17.51 +/- 0.17 u 298 547 246 17.33 +/- 0.06 w1 679 2173 175 >19.6 m2 654 2496 214 >19.6 w2 605 2447 214 >20.0 The magnitudes in the table are not corrected for the significant Galactic extinction due to the reddening of E(B-V) = 0.31 in the direction of the burst (Schlegel et al. 1998).