{
  "circularId": 40467,
  "eventId": "GRB 250516A",
  "createdOn": 1747407428286,
  "submittedHow": "email",
  "submitter": "K.L. Page at U Leicester <klp5@leicester.ac.uk>",
  "bibcode": "2025GCN.40467....1B",
  "body": "A. P. Beardmore (U Leicester), P. A. Evans (U Leicester),\nR. Gupta (NASA GSFC), K. L. Page (U Leicester),\nS. P. R. Shilling (Lancaster U.) and M. A. Williams (PSU) report on\nbehalf of the Neil Gehrels Swift Observatory Team:\n\nAt 14:35:29 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 250516A (trigger=1314210). Swift slewed immediately to the burst.\nThe BAT on-board calculated location is RA, Dec 334.561, -9.130 which is \n   RA(J2000) = 22h 18m 15s\n   Dec(J2000) = -09d 07' 48\"\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 ~5000 counts/sec (15-350 keV), at ~5 sec after the trigger.\n\nThe XRT began observing the field at 14:37:13.2 UT, 104.3 seconds after\nthe BAT trigger. Using promptly downlinked data we find a fading,\nuncatalogued X-ray source with an enhanced position: RA, Dec 334.60979,\n-9.11941 which is equivalent to:\n   RA(J2000)  = 22h 18m 26.35s\n   Dec(J2000) = -09d 07' 09.9\"\nwith an uncertainty of 1.9 arcseconds (radius, 90% containment). This\nlocation is 177 arcseconds from the BAT onboard position, within the\nBAT error circle. This position may be improved as more data are\nreceived; the latest position is available at\nhttps://www.swift.ac.uk/sper. \n\nA power-law fit to a spectrum formed from promptly downlinked event\ndata gives a column density in excess of the Galactic value (5.84 x\n10^20 cm^-2, Willingale et al. 2013), with an excess column of 1.8\n(+1.47/-1.34) x 10^21 cm^-2 (90% confidence).\n\nUVOT took a finding chart exposure of 150 seconds with the White filter\nstarting 108 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 none of\nthe XRT error circle. The 8'x8' region for the list of sources generated\non-board covers 100% of the XRT error circle. The list of sources is typically\ncomplete to about 18 mag. No correction has been made for the expected\nextinction corresponding to E(B-V) of 0.062.\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",
  "subject": "GRB 250516A: Swift detection of a burst"
}