TITLE: GCN CIRCULAR NUMBER: 40840 SUBJECT: GRB 250625A: Swift/UVOT Upper Limits DATE: 25/06/26 11:21:27 GMT FROM: Alice Breeveld at MSSL-UCL <a.breeveld@ucl.ac.uk> A.A. Breeveld (UCL-MSSL) and M. Ferro (INAF-OAB) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250625A 125 s after the BAT trigger (Ferro et al., GCN Circ. 40825). The optical afterglow reported by Moskvitin et al. (GCN Circ. 40828), Xin et al. (GCN Cir. 40830), Zhu et al. (GCN Circ. 40834) Fortin et al. (GCN Circ. 40837), Adami et al. (GCN Circ. 40838) and Brosio et al. (GCN Circ. 40839) is not 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 125 275 147 >20.9 u_FC 283 533 246 >20.5 white 125 1529 392 >21.7 v 613 1579 117 >19.2 b 539 1505 97 >20.4 u 283 1480 324 >20.6 w1 662 1628 117 >19.6 m2 637 1431 78 >20.1 w2 589 1383 97 >20.6 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.054 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/40840. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...