TITLE: GCN CIRCULAR NUMBER: 30256 SUBJECT: GRB 210618A: Swift/UVOT Upper Limits DATE: 21/06/18 22:41:20 GMT FROM: Paul Kuin at MSSL N. P. M. Kuin (UCL-MSSL) and M. G. Bernardini (INAF-OAB) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 210618A 3728 s after the BAT trigger (Bernardini et al., GCN Circ. 30250). No optical afterglow consistent with the XRT candidates source 1, 2 or 4 (Osborne et al. , GCN Circ. 30252) 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 3728 3878 147 >20.4 white 3728 4496 344 >21.1 v 4707 4843 133 >19.2 b 4092 4291 197 >20.5 u 3886 4086 197 >20.0 w2 4502 4702 197 >20.1 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.015 in the direction of the burst (Schlegel et al. 1998). Since this is a short GRB, further Swift search for late time optical emission is being planned.