TITLE: GCN CIRCULAR NUMBER: 29787 SUBJECT: GRB 210410A: Swift/UVOT Upper Limits DATE: 21/04/10 21:16:09 GMT FROM: Paul Kuin at MSSL Paul Kuin (MSSL/UCL) and A. Melandri(INAF-OAB) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 210410A (trigger 01042113; previously reported by Fermi/GBM in GCN #29777) 1113 s after the Fermi trigger at 2021-04-10 00:53:16 UT. No optical afterglow consistent with the XRT position (Melandri et al. GCN Circ. 29778) 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 3-sigma UL v 1129 1149 19 >17.0 b 5021 5109 85 >19.7 u 4817 5014 197 >19.9 w1 4610 4809 197 >19.3 m2 4403 4602 197 >19.4 w2 1113 1125 12 >17.0 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.05 in the direction of the burst (Schlegel et al. 1998).