{
  "bibcode": "2025GCN.41511....1S",
  "submitter": "K.L. Page at U Leicester <klp5@leicester.ac.uk>",
  "body": "M. H. Siegel (PSU), S. Dichiara (PSU), R. Gupta (NASA GSFC),\nN. P. M. Kuin (UCL-MSSL), S. Lanava (PSU), K. L. Page (U Leicester),\nD. M. Palmer (LANL) and B. Sbarufatti (INAF-OAB) report on behalf of\nthe Neil Gehrels Swift Observatory Team:\n\nAt 20:10:07 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 250823A (trigger=1344586).  Swift slewed immediately to the burst.\nThe BAT on-board calculated location is \nRA, Dec 297.521, -24.976 which is \n   RA(J2000) = 19h 50m 05s\n   Dec(J2000) = -24d 58' 33\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty). The BAT light curve shows a complex structure \nwith a duration of 200 sec.  The peak count rate\nwas ~1600 counts/sec (15-350 keV), at ~4 sec after the trigger.\n\nThe XRT began observing the field at 20:17:28.0 UT, 440.5 seconds after\nthe BAT trigger. Using promptly downlinked data we find a fading,\nuncatalogued X-ray source with an enhanced position: RA, Dec 297.47788,\n-24.99582 which is equivalent to:\n   RA(J2000)  = 19h 49m 54.69s\n   Dec(J2000) = -24d 59' 45.0\"\nwith an uncertainty of 2.1 arcseconds (radius, 90% containment). This\nlocation is 157 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 (1.12 x\n10^21 cm^-2, Willingale et al. 2013), with an excess column of 3.9\n(+3.01/-2.59) x 10^21 cm^-2 (90% confidence).\n\nUVOT took a finding chart exposure of 250 seconds with the U filter starting\n338 seconds after the BAT trigger. No credible afterglow candidate has been\nfound in the initial data products. The 2.7'x2.7' sub-image covers 100% of the\nXRT error circle. The typical 3-sigma upper limit has been about 19.2 mag. The\n8'x8' region for the list of sources generated on-board covers 100% of the XRT\nerror circle. The list of sources is typically complete to about 18.0 mag. No\ncorrection has been made for the expected extinction corresponding to E(B-V) of\n0.111.\n\nSome data, such as earlier XRT observations, are not available due to\na telemetry gap, and will be produced on the full ground download.\n\nBurst Advocate for this burst is M. H. Siegel (siegel AT swift.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",
  "subject": "GRB 250823A: Swift detection of a burst",
  "submittedHow": "email",
  "circularId": 41511,
  "createdOn": 1755981095478,
  "eventId": "GRB 250823A"
}