TITLE: GCN CIRCULAR NUMBER: 40009 SUBJECT: GRB 250327B: Swift/UVOT Detection DATE: 25/04/02 13:32:05 GMT FROM: Mike Siegel at PSU/Swift MOC <mhs18@psu.edu> M.H. Siegel (PSU) reports on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250327B 1753 s after the SVOM trigger sb25032706 (GCN Circ. 39888). A fading source consistent with the XRT position (Page et al., GCN Circ. 39895) and the optical counterpart (Moskvitin et al., GCN Circ. 39889; Xin et al., GCN Circ. 39890; O’Neill et al., GCN Circ. 39891; Lian et al., GCN Circ. 39894; Shrestha et al., GCN Circ. 39896; Ducoin et al., GCN Circ. 39897; Perley & Bochenek; GCN Circ. 39902; Kumar et al., GCN Circ. 39904; Dennefeld et al., GCN circ. 39905; Pankov et al., GCN circ. 39906) is detected in the initial UVOT exposures. Preliminary detections and 3-sigma upper limits for the early exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag(AB) u 1753 2505 740 19.78+/-0.18 u 91894 113326 2601 >21.28 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.018 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/40009. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...