TITLE: GCN CIRCULAR NUMBER: 41920 SUBJECT: GRB 250920C: Swift/UVOT Detection DATE: 25/09/20 21:48:29 GMT FROM: Paul Kuin at MSSL <npkuin@gmail.com> N. P. M. Kuin (UCL-MSSL) and R. Gupta (GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250920C 124 s after the BAT trigger (Gupta et al., GCN Circ. 41904). A source consistent with the XRT position is detected in the initial UVOT exposures. The preliminary UVOT position is: RA (J2000)= 03h 25m 51.76s, 51.46568 deg Dec (J2000) = -29d 39m 20.2s, -29.65562 deg consistent with the detection by GOTO (Wortley et al. GCN Circ. 41907). 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 146 207 60.5 14.55 +/- 0.04 v 124 133 10.1 14.56 +/- 0.09 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.019 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/41920. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...