{
  "circularId": 42070,
  "bibcode": "2025GCN.42070....1B",
  "createdOn": 1759457450915,
  "submittedHow": "email",
  "subject": "GRB 251003A: Swift detection of a burst",
  "submitter": "K.L. Page at U Leicester <klp5@leicester.ac.uk>",
  "eventId": "GRB 251003A",
  "body": "A. P. Beardmore (U Leicester), R. Gupta (NASA GSFC),\nK. L. Page (U Leicester) and M. H. Siegel (PSU) report on behalf of\nthe Neil Gehrels Swift Observatory Team:\n\nAt 01:58:30 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 251003A (trigger=1400964).  Swift slewed immediately to the burst.\nThe BAT on-board calculated location is \nRA, Dec 18.503, +56.507 which is \n   RA(J2000) = 01h 14m 01s\n   Dec(J2000) = +56d 30' 23\"\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 20 sec.  The peak count rate\nwas ~1835 counts/sec (15-350 keV), at ~0 sec after the trigger.\n\nThe XRT began observing the field at 01:59:42.1 UT, 72.1 seconds after\nthe BAT trigger. Using promptly downlinked data we find a bright,\nfading, uncatalogued X-ray source located at RA, Dec 18.52734, 56.49009\nwhich is equivalent to:\n   RA(J2000)  = 01h 14m 06.56s\n   Dec(J2000) = +56d 29' 24.3\"\nwith an uncertainty of 3.8 arcseconds (radius, 90% containment). This\nlocation is 77 arcseconds from the BAT onboard position, within the BAT\nerror circle. This position may be improved as more data are received;\nthe latest position is available at https://www.swift.ac.uk/sper. \n\nA power-law fit to a spectrum formed from promptly downlinked event\ndata gives a column density consistent with the Galactic value of 4.39\nx 10^21 cm^-2 (Willingale et al. 2013). \n\nThe initial flux in the 2.5 s image was 1.66e-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 78 seconds after the BAT trigger. No credible afterglow candidate has\nbeen found in the initial data products. The 2.7'x2.7' sub-image covers 100% of\nthe XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag.\nThe 8'x8' region for the list of sources generated on-board covers 100% of the\nXRT error circle. The list of sources is typically complete to about 18 mag. No\ncorrection has been made for the expected extinction corresponding to E(B-V) of\n0.408.\n\nBurst Advocate for this burst is A. P. Beardmore (apb AT star.le.ac.uk).\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"
}