{
  "subject": "GRB 250424A: Swift/UVOT Detection",
  "submitter": "Mike Siegel at PSU/Swift MOC <mhs18@psu.edu>",
  "submittedHow": "web",
  "format": "text/plain",
  "circularId": 40244,
  "eventId": "GRB 250424A",
  "body": "M.H. Siegel (PSU) and S. B. Cenko (GSFC) report on behalf of the Swift/UVOT team:\n\nThe Swift/UVOT began settled observations of the field of GRB 250424A 254 s after the BAT trigger (Cenko et al., GCN Circ. 40224). A source consistent with the XRT position (Evans et al., GCN Circ. 40232) and the optical transient (Francile et al., GCN Circ. 40222, Brivio et al., GCN Circ. 40225; Becerra et al., GCN Circ. 40226; de Wet et al., GCN Circ. 40229; Ducoin et al., GCN Circ. 40230; Turpin et al., GCN Circ. 40240; Dutton et al., GCN Circ. 40241) is detected in the initial UVOT exposures.\n\nThe preliminary UVOT position is:\n    RA  (J2000) =  14:29:60.00 = 217.49998 (deg.)\n    Dec (J2000) = -35:01:30.6  = -35.02518 (deg.)\nwith an estimated uncertainty of 0.47 arc sec. (radius, 90% confidence).\n\nPreliminary detections and 3-sigma upper limits using the UVOT photometric system\n(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              254          404          147         18.96 +/- 0.07\nv                  411         1918          175        >18.7\nb                  509         1844          136         19.97 +/- 0.26\nu                  485         1647          136         19.15 +/- 0.20\nw1                 460         1795          156         19.44 +/- 0.31\nm2                 436         1598           97        >18.4\nw2                 559         1894          156        >19.9\n\nThe magnitudes in the table are not corrected for the Galactic extinction\ndue to the reddening of E(B-V) = 0.064 in the direction of the burst\n(Schlegel et al. 1998).",
  "bibcode": "2025GCN.40244....1S",
  "createdOn": 1745536161010
}