{
  "body": "\nT. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB), S. Dichiara (PSU),\nM. Ferro (INAF-OAB), J.D. Gropp (PSU), S. Laha (GSFC/UMBC),\nM. J. Moss (GSFC), K. L. Page (U Leicester), D. M. Palmer (LANL),\nB. Sbarufatti (INAF-OAB) and M. H. Siegel (PSU) report on behalf of\nthe Neil Gehrels Swift Observatory Team:\n\nAt 18:35:42 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 231216A (trigger=1202749).  Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA, Dec 39.759, +33.596 which is \n   RA(J2000) = 02h 39m 02s\n   Dec(J2000) = +33d 35' 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 70 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 18:37:53.1 UT, 131.1 seconds after\nthe BAT trigger. Using promptly downlinked data we find a fading,\nuncatalogued X-ray source located at RA, Dec 39.77287, 33.57671 which\nis equivalent to:\n   RA(J2000)  = 02h 39m 05.49s\n   Dec(J2000) = +33d 34' 36.2\"\nwith an uncertainty of 3.9 arcseconds (radius, 90% containment). This\nlocation is 80 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 8.36\nx 10^20 cm^-2 (Willingale et al. 2013). \n\nUVOT took a finding chart exposure of 250 seconds with the U filter starting\n191 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 33% of the\nXRT error circle. The typical 3-sigma upper limit has been about 19.2 mag. \nResults from the list of sources generated on-board are not available at this\ntime. No correction has been made for the expected extinction corresponding to\nE(B-V) of 0.081. \n\nBurst Advocate for this burst is T. Sbarrato (tullia.sbarrato AT inaf.it). \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",
  "bibcode": "2023GCN.35378....1S",
  "submitter": "Tullia Sbarrato at INAF-OAB <tullia.sbarrato@inaf.it>",
  "eventId": "GRB 231216A",
  "circularId": 35378,
  "createdOn": 1702752967244,
  "subject": "GRB 231216A: Swift detection of a burst",
  "submittedHow": "email"
}