{
  "createdOn": 1738892093520,
  "subject": "GRB 250207A: Swift detection of a burst with optical counterpart",
  "body": "M. Ferro (INAF-OAB), R. Gupta (NASA GSFC), J. A. Kennea (PSU),\nK. L. Page (U Leicester) and B. Sbarufatti (INAF-OAB) report on behalf\nof the Neil Gehrels Swift Observatory Team:\n\nAt 01:16:07 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 250207A (trigger=1287821).  Swift slewed immediately to the burst.\nThe BAT on-board calculated location is \nRA, Dec 16.115, -12.159 which is \n   RA(J2000) = 01h 04m 28s\n   Dec(J2000) = -12d 09' 30\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The BAT light curve showed a complex \nstructure with a duration of about 30 sec.  The peak count rate\nwas ~3847 counts/sec (15-350 keV), at ~6 sec after the trigger.\n\nThe XRT began observing the field at 01:17:53.2 UT, 105.9 seconds after\nthe BAT trigger. XRT found a bright, uncatalogued X-ray source located\nat RA, Dec 16.0892, -12.1633 which is equivalent to:\n   RA(J2000)  = 01h 04m 21.41s\n   Dec(J2000) = -12d 09' 47.9\"\nwith an uncertainty of 5.9 arcseconds (radius, 90% containment). This\nlocation is 92 arcseconds from the BAT onboard position, within the BAT\nerror circle. Despite the onboard localisation, no X-ray source was\ndetected in 85 s of promptly-downlinked data, suggesting that the\ninitial centroid may equally have been a cosmic ray. This position\nshould\ttherefore be treated with caution. \n\nThe initial flux in the 2.5 s image was 7.54e-10 erg cm^-2 s^-1 (0.2-10\nkeV).\n\nUVOT took a finding chart exposure of 150 seconds with the White filter\nstarting 113 seconds after the BAT trigger. There is a candidate afterglow in\nthe rapidly available 2.7'x2.7' sub-image at\n  RA(J2000)  =\t01:04:21.41 =  16.08919\n  DEC(J2000) = -12:09:52.5  = -12.16458\nwith a 90%-confidence error radius of about 0.74 arc sec. This position is 4.6\narc sec. from the center of the XRT error circle. The estimated magnitude is\n15.04 with a 1-sigma error of about  0.14. No correction has been made for the\nexpected extinction corresponding to E(B-V) of 0.027.\n\nBurst Advocate for this burst is M. Ferro (matteo.ferro AT inaf.it).\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",
  "bibcode": "2025GCN.39182....1F",
  "submitter": "Jamie Kennea at Penn State <jak51@psu.edu>",
  "submittedHow": "email",
  "circularId": 39182,
  "eventId": "GRB 250207A"
}