TITLE: GCN CIRCULAR NUMBER: 41721 SUBJECT: GRB 250904A: Swift/UVOT Detection DATE: 25/09/05 10:09:45 GMT FROM: Samantha Oates at University of Birmingham <samantha.oates@alumni.ucl.ac.uk> S. R. Oates (Lancaster Uni.) and C. Salvaggio (INAF-OAB) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250904A 86 s after the BAT trigger (Salvaggio et al., GCN Circ. 41704). A source consistent with the XRT position (Goad et al., GCN Circ. 41711) is detected in white and marginally in u. Preliminary detections and 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag/3sigUL white (FC) 86 235 147 20.23+\-0.36 u (FC) 298 441 141 19.14+\-0.41 (2.7 sigma) white 4990 10603 1097 20.60+\-0.16 v 5401 5601 197 >19.5 b 4786 6421 393 >20.4 u 6016 6215 197 >19.6 uvw1 5811 6011 197 >19.5 uvm2 5606 5806 197 >19.4 uvw2 5196 10942 524 >20.2 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.284 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/41721. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...