TITLE: GCN CIRCULAR NUMBER: 21099 SUBJECT: GRB 170516A: Swift/UVOT Upper Limits DATE: 17/05/16 22:02:21 GMT FROM: Paul Kuin at MSSL N. P. M. Kuin (UCL-MSSL) 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 170516A 87 s after the BAT trigger (Lien et al., GCN Circ. 21097). No optical afterglow consistent with the XRT position (Lien et al. GCN Circ. 21097) 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 87 237 147 >20.1 white 87 5703 541 >21.1 v 4478 6113 393 >19.8 b 3863 5498 393 >20.6 u 299 5293 379 >19.4 w1 4888 5088 197 >19.4 m2 4683 6222 299 >20.5 w2 4274 5909 393 >20.5 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.03 in the direction of the burst (Schlegel et al. 1998).