TITLE: GCN CIRCULAR NUMBER: 41316 SUBJECT: GRB 250809A: Swift/UVOT Detection DATE: 25/08/10 16:51:32 GMT FROM: Paul Kuin at MSSL <npkuin@gmail.com> N.P.M. Kuin (UCL/MSSL) and T. M. Parsotan (GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250809A 128 s after the BAT trigger (Parsotan et al., GCN Circ. 41303). A source consistent with the XRT position ( Evans et al. GCN Circ. 41304 ) 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 v 435 755 58 17.62 +/- 0.21 b 384 1038 97 18.86 +/- 0.19 u 128 1013 452 19.57 +/- 0.21 w1 484 805 58 >18.4 m2 459 780 58 >20.1 w2 410 1064 78 >18.8 The earliest exposures were fainter; these detections are near the peak of the light curve. The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 1.919 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/41316. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...