TITLE: GCN CIRCULAR NUMBER: 28475 SUBJECT: GRB 200917A: Swift/UVOT Upper Limits DATE: 20/09/22 20:13:27 GMT FROM: Kira Simpson at PSU GRB 200917A: Swift/UVOT Upper Limits K. K. Simpson (PSU) and E. Sonbas (Adiyaman Univ.) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 200917A 104 s after the BAT trigger (Sonbas et al., GCN Circ. 28435). No optical afterglow consistent with the XRT position (Goad et al. GCN Circ. 28436) 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 104 254 147 >19.9 u_FC 262 512 246 >20.1 white 104 1708 412 >20.5 v 592 1758 136 >18.9 b 518 1684 117 >19.5 u 262 1832 382 >20.2 w1 641 1807 136 >18.7 m2 1762 1782 19 >18.2 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.19 in the direction of the burst (Schlegel et al. 1998).