{
  "body": "N. J. Klingler (GSFC/UMBC/CRESSTII), R. Brivio (INAF-OAB),\nJ. J. DeLaunay (PSU), R. Gupta (NASA GSFC), J. A. Kennea (PSU),\nK. L. Page (U Leicester) and C. Salvaggio (INAF-OAB) report on behalf\nof the Neil Gehrels Swift Observatory Team:\n\nAt 10:46:08.44 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 250807A (trigger=1340514). Swift slewed immediately to the burst.\nThe BAT on-board calculated location is RA, Dec 51.420, -47.877 which is \n   RA(J2000) = 03h 25m 41s\n   Dec(J2000) = -47d 52' 38\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The BAT light curve showed a complex structure \nwith a duration of about 80 sec.  The peak count rate\nwas ~19000 counts/sec (15-350 keV), at ~35 sec after the trigger.\n\nThe XRT began observing the field at 10:47:49.5 UT, 101.1 seconds after\nthe BAT trigger. XRT found a bright, uncatalogued X-ray source located\nat RA, Dec 51.4478, -47.8880 which is equivalent to:\n   RA(J2000)  = 03h 25m 47.47s\n   Dec(J2000) = -47d 53' 16.8\"\nwith an uncertainty of 4.8 arcseconds (radius, 90% containment). This\nlocation is 77 arcseconds from the BAT onboard position, within the BAT\nerror circle. No event data are yet available to determine the column\ndensity using X-ray spectroscopy.\n\nUVOT took a finding chart exposure of 150 seconds with the White filter\nstarting 111 seconds after the BAT trigger. There is a candidate afterglow in\nthe rapidly available 2.7'x2.7' sub-image at\n  RA(J2000)  =\t03:25:47.59 =  51.44829\n  DEC(J2000) = -47:53:16.2  = -47.88782\nwith a 90%-confidence error radius of about 0.75 arc sec. This position is 1.3\narc sec. from the center of the XRT error circle. The estimated magnitude is\n17.98 with a 1-sigma error of about  0.14. No correction has been made for the\nexpected extinction corresponding to E(B-V) of 0.011.\n\nBurst Advocate for this burst is N. J. Klingler (noelklin AT umbc.edu).\nPlease contact the BA by email if you require additional information\nregarding Swift followup of this burst. In extremely urgent cases, after\ntrying the Burst Advocate, you can contact the Swift PI by phone (see\nSwift TOO web site for information: http://www.swift.psu.edu/)\n\n",
  "createdOn": 1754564616030,
  "bibcode": "2025GCN.41262....1K",
  "eventId": "GRB 250807A",
  "circularId": 41262,
  "submittedHow": "email",
  "subject": "GRB 250807A: Swift detection of a burst with an optical counterpart",
  "submitter": "noelklin@umbc.edu"
}