{
  "bibcode": "2025GCN.41316....1K",
  "circularId": 41316,
  "submittedHow": "email",
  "createdOn": 1754844692725,
  "subject": "GRB 250809A: Swift/UVOT Detection",
  "body": "N.P.M. Kuin (UCL/MSSL) and T. M. Parsotan (GSFC) report on behalf of the\nSwift/UVOT team:\n\nThe Swift/UVOT began settled observations of the field of GRB 250809A\n128 s after the BAT trigger (Parsotan et al., GCN Circ. 41303). A source\nconsistent with the XRT position ( Evans et al. GCN Circ. 41304 ) is\ndetected in the initial UVOT exposures.\n\nPreliminary detections and 3-sigma upper limits using the UVOT photometric\nsystem (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early\nexposures are:\n\nFilter         T_start(s)   T_stop(s)      Exp(s)           Mag\n\nv                  435          755           58         17.62 +/- 0.21\nb                  384         1038           97         18.86 +/- 0.19\nu                  128         1013          452         19.57 +/- 0.21\nw1                 484          805           58        >18.4\nm2                 459          780           58        >20.1\nw2                 410         1064           78        >18.8\n\nThe earliest exposures were fainter; these detections are near the peak of\nthe light curve.\n\nThe magnitudes in the table are not corrected for the Galactic extinction due\nto the reddening of E(B-V) = 1.919 in the direction of the burst (Schlegel\net al. 1998).\n",
  "eventId": "GRB 250809A",
  "submitter": "Paul Kuin at MSSL <npkuin@gmail.com>"
}