TITLE: GCN CIRCULAR NUMBER: 17085 SUBJECT: GRB 141121A: Swift/UVOT Detections DATE: 14/11/21 19:03:15 GMT FROM: Frank Marshall at GSFC F. E. Marshall (NASA/GSFC) and A. Y. Lien (GSFC/UMBC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 141121A 371 s after the BAT trigger (Lien et al., GCN Circ. 17075). A source consistent with the optical position (Tanga et al. GCN Circ. 17078) is detected in the initial UVOT exposures. The preliminary UVOT position is: RA (J2000) = 08:10:40.63 = 122.66928 (deg.) Dec (J2000) = 22:13:02.2 = 22.21728 (deg.) with an estimated uncertainty of 0.5 arcsec. (radius, 90% confidence). The source shows an unusual light curve with little evidence for variability. The source is detected in all UVOT filters although the detections in v and w2 are not highly significant. 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 371 520 147 >20.1 white 6067 6266 197 20.2 +/- 0.2 v 527 547 19 >18.3 v 15373 16025 635 20.3 +/- 0.3 b 5862 6062 197 19.8 +/- 0.2 u 5562 5714 149 19.4 +/- 0.2 u 27756 28325 556 19.3 +/- 0.1 w1 3830 3897 66 19.4 +/- 0.3 w1 26850 27750 886 19.7 +/- 0.1 m2 21039 21939 886 20.4 +/- 0.2 w2 9514 12083 771 21.2 +/- 0.3 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.05 in the direction of the burst (Schlegel et al. 1998).