{
  "circularId": 35436,
  "submitter": "K.L. Page at U Leicester <klp5@leicester.ac.uk>",
  "eventId": "GRB 231230A",
  "bibcode": "2023GCN.35436....1M",
  "createdOn": 1703900658342,
  "submittedHow": "email",
  "subject": "GRB 231230A: Swift detection of a burst",
  "body": "\nM. J. Moss (GSFC), C. Gronwall (PSU), J.D. Gropp (PSU),\nH. A. Krimm (NSF), A. Y. Lien (U Tampa), K. L. Page (U Leicester) and\nM. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift\nObservatory Team:\n\nAt 01:29:08 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 231230A (trigger=1205319).  Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA, Dec 245.197, +58.120 which is \n   RA(J2000) = 16h 20m 47s\n   Dec(J2000) = +58d 07' 11\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The BAT light curve showed a multi-peaked\nstructure with a duration of about 30 sec.  The peak count rate\nwas ~1500 counts/sec (15-350 keV), at ~1 sec after the trigger. \n\nThe XRT began observing the field at 01:32:45.0 UT, 216.3 seconds after\nthe BAT trigger. Using promptly downlinked data we find an uncatalogued\nX-ray source located at RA, Dec 245.21706, 58.12324 which is equivalent\nto:\n   RA(J2000)  = 16h 20m 52.09s\n   Dec(J2000) = +58d 07' 23.7\"\nwith an uncertainty of 3.5 arcseconds (radius, 90% containment). This\nlocation is 39 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.  We\ncannot determine whether the source is fading at the present time. \n\nA power-law fit to a spectrum formed from promptly downlinked event\ndata gives a column density in excess of the Galactic value (1.31 x\n10^20 cm^-2, Willingale et al. 2013), with an excess column of 4.3\n(+4.82/-3.83) x 10^21 cm^-2 (90% confidence). \n\nUVOT took a finding chart exposure of 150 seconds with the White filter\nstarting 145 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\n0.015. \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"
}