{
  "eventId": "GRB 251201B",
  "subject": "GRB 251201B: Swift detection of a burst with an optical counterpart",
  "createdOn": 1764607088832,
  "submitter": "Tyler Parsotan  at NASA GSFC <tyler.parsotan@nasa.gov>",
  "circularId": 42924,
  "bibcode": "2025GCN.42924....1M",
  "body": "M. J. Moss (GSFC), S. Dichiara (PSU), R. Gupta (NASA GSFC),\nJ. A. Kennea (PSU), K. L. Page (U Leicester) and T. M. Parsotan (GSFC)\nreport on behalf of the Neil Gehrels Swift Observatory Team:\n\nAt 16:26:30 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 251201B (trigger=1418729).  Swift slewed immediately to the burst.\nThe BAT on-board calculated location is \nRA, Dec 6.409, -44.237 which is \n   RA(J2000) = 00h 25m 38s\n   Dec(J2000) = -44d 14' 12\"\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 40 sec.  The peak count rate\nwas ~2000 counts/sec (15-350 keV), at ~0 sec after the trigger.\n\nThe XRT began observing the field at 16:28:03.7 UT, 93.4 seconds after\nthe BAT trigger. XRT found a bright, uncatalogued X-ray source located\nat RA, Dec 6.3925, -44.2312 which is equivalent to:\n   RA(J2000)  = 00h 25m 34.20s\n   Dec(J2000) = -44d 13' 52.3\"\nwith an uncertainty of 7.0 arcseconds (radius, 90% containment). This\nlocation is 47 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\nThe initial flux in the 0.1 s image was 8.63e-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 101 seconds after the BAT trigger. There is a candidate afterglow in\nthe rapidly available 2.7'x2.7' sub-image at\n  RA(J2000)  =\t00:25:34.59 =\t6.39413\n  DEC(J2000) = -44:14:01.1  = -44.23364\nwith a 90%-confidence error radius of about 0.75 arc sec. This position is 9.7\narc sec. from the center of the XRT error circle. The estimated magnitude is\n17.28 with a 1-sigma error of about  0.14. No correction has been made for the\nexpected extinction corresponding to E(B-V) of 0.008.\n\nBurst Advocate for this burst is M. J. Moss (mikejmoss3 AT gmail.com).\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",
  "submittedHow": "email"
}