TITLE: GCN CIRCULAR NUMBER: 41521 SUBJECT: GRB 250823A: Swift/UVOT Detection DATE: 25/08/24 09:33:50 GMT FROM: Paul Kuin at MSSL <npkuin@gmail.com> Paul Kuin (UCL/MSSL) and M. H. Siegel (PSU) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250823A 126 s after the BAT trigger (Siegel et al., GCN Circ. 41511). A source consistent with the XRT position is detected in the initial UVOT exposures. 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 white 126 1020 334 20.42 +/- 0.17 v 668 1244 78 18.43 +/- 0.28 b 594 1169 58 19.25 +/- 0.28 u 338 1317 304 >19.5 w1 718 1293 58 >19.1 m2 692 1268 58 >18.8 w2 644 1391 97 >19.3 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.111 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/41521. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...