{
  "body": "A.A. Breeveld (UCL-MSSL) and T. M. Parsotan (GSFC) report on behalf of the Swift/UVOT team:\n\nThe Swift/UVOT began settled observations of the field of GRB 250430A 118 s after the BAT trigger (Parsotan et al., GCN Circ. 40292).\nThe 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.\n\nPreliminary 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:\n\nFilter         T_start(s)   T_stop(s)      Exp(s)           Mag\n\nwhite_FC           141          291          147         19.08 ± 0.1\nwhite              843         1856          264         19.40 ± 0.1\nv                  118         1733          169        >18.9\nb                  473         1831          156        >19.8\nu                  448          468           20         17.91 ± 0.3\nu                  621         1117           59         18.67 ± 0.3\nw1                 424         1782          156        >19.0\nm2                1393         1413           19        >17.3\nw2                 696         1364           58        >18.6\n\nThe 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).\n",
  "submittedHow": "email",
  "createdOn": 1746188522553,
  "submitter": "Alice Breeveld at MSSL-UCL <a.breeveld@ucl.ac.uk>",
  "subject": "GRB 250430A: Swift/UVOT Detection",
  "bibcode": "2025GCN.40321....1B",
  "circularId": 40321,
  "eventId": "GRB 250430A"
}