TITLE: GCN CIRCULAR NUMBER: 19568 SUBJECT: GRB 160623A: Swift/UVOT Upper Limits DATE: 16/06/24 19:31:52 GMT FROM: Alice Breeveld at MSSL-UCL Alice Breeveld (UCL-MSSL) and A. Maselli (INAF-IASFPA) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 160623A 40254 s after the LAT trigger (Vianello et al., GCN Circ. 19553). No optical afterglow consistent with the XRT position (Mingo et al. GCN Circ. 19558) or the Mondy and RATIR position (Pozanenko et al. GCN Circ. 19561; Butler et al. GCN Circ. 19567) 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 initial exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag v 40657 51652 2859 >21.1 u 40254 51253 2008 >21.5 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 1.35 in the direction of the burst (Schlegel et al. 1998).