{
  "eventId": "GRB 251205A",
  "subject": "GRB 251205A: Swift detection of a burst with an optical afterglow",
  "submittedHow": "email",
  "body": "S. Lanava (PSU), S. Dichiara (PSU), C. Gronwall (PSU),\nR. Gupta (NASA GSFC), N. P. M. Kuin (UCL-MSSL), A. Y. Lien (U Tampa),\nD. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the\nNeil Gehrels Swift Observatory Team:\n\nAt 23:39:47 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 251205A (trigger=1420873).  Swift slewed immediately to the burst.\nThe BAT on-board calculated location is \nRA, Dec 200.243, +29.962 which is \n   RA(J2000) = 13h 20m 58s\n   Dec(J2000) = +29d 57' 45\"\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 ~500 counts/sec (15-350 keV), at ~0 sec after the trigger.\n\nThe XRT began observing the field at 23:42:07.0 UT, 139.8 seconds after\nthe BAT trigger. XRT found a bright, uncatalogued X-ray source located\nat RA, Dec 200.2707, 29.9296 which is equivalent to:\n   RA(J2000)  = 13h 21m 4.97s\n   Dec(J2000) = +29d 55' 46.6\"\nwith an uncertainty of 5.3 arcseconds (radius, 90% containment). This\nlocation is 145 arcseconds from the BAT onboard position, within the\nBAT error circle. No event data are yet available to determine the\ncolumn density using X-ray spectroscopy.\n\nThe initial flux in the 2.5 s image was 1.44e-09 erg cm^-2 s^-1 (0.2-10\nkeV).\n\nUVOT took a finding chart exposure of 150 seconds with the White filter\nstarting 148 seconds after the BAT trigger. There is a candidate afterglow in\nthe rapidly available 2.7'x2.7' sub-image at\n  RA(J2000)  =\t13:21:05.34 = 200.27223\n  DEC(J2000) = +29:55:44.0  =  29.92888\nwith a 90%-confidence error radius of about 0.75 arc sec. This position is 5.4\narc sec. from the center of the XRT error circle. The estimated magnitude is\n17.54 with a 1-sigma error of about  0.14. No correction has been made for the\nexpected extinction corresponding to E(B-V) of 0.014.\n\nBurst Advocate for this burst is S. Lanava (sml7284 AT psu.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",
  "circularId": 43005,
  "submitter": "David Palmer at LANL <palmer@lanl.gov>",
  "createdOn": 1764979359436,
  "bibcode": "2025GCN.43005....1L"
}