TITLE: GCN CIRCULAR NUMBER: 19217 SUBJECT: GRB 160321A: Swift/UVOT Upper Limits DATE: 16/03/22 15:04:48 GMT FROM: Sam Emery at MSSL-UCL S.W.K. Emery (UCL-MSSL) and M. Stamatikos (OSU/NASA/GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 160321A 115 s after the BAT trigger (Stamatikos et al., GCN Circ. 19211). No optical afterglow consistent with the XRT position (Beardmore et al. GCN Circ. 19213) is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white_FC 115 265 147 >20.4 u_FC 273 523 246 >19.7 white 115 6458 546 >21.1 v 603 6870 452 >19.5 b 529 6253 255 >20.1 u 273 12683 570 >20.1 w1 652 12607 1141 >20.2 m2 627 11700 1205 >20.1 w2 579 6664 452 >19.7 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.75 in the direction of the burst (Schlegel et al. 1998).