TITLE: GCN CIRCULAR NUMBER: 40321 SUBJECT: GRB 250430A: Swift/UVOT Detection DATE: 25/05/02 12:22:02 GMT FROM: Alice Breeveld at MSSL-UCL <a.breeveld@ucl.ac.uk> A.A. Breeveld (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 250430A 118 s after the BAT trigger (Parsotan et al., GCN Circ. 40292). The optical source detected in the UVOT white filter reported in that circular (and also detected by Oden & Guessoum, GCN Circ. 40295; Garnichy et al., GCN Circ. 40301; Komesh et al., GCN Circ. 40307; Zheng et al., GCN Circ. 40310 and Li et al., GCN Circ. 40311) was also detected in the UVOT U-band filter, but has since faded. 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_FC 141 291 147 19.08 ± 0.1 white 843 1856 264 19.40 ± 0.1 v 118 1733 169 >18.9 b 473 1831 156 >19.8 u 448 468 20 17.91 ± 0.3 u 621 1117 59 18.67 ± 0.3 w1 424 1782 156 >19.0 m2 1393 1413 19 >17.3 w2 696 1364 58 >18.6 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.092 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/40321. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...