{
  "bibcode": "2021GCN.31316....1B",
  "body": "A. P. Beardmore (U Leicester), S. D. Barthelmy (GSFC),\nF. E. Marshall (NASA/GSFC), K. L. Page (U Leicester),\nD. M. Palmer (LANL), T. M. Parsotan (GSFC/UMBC/CRESSTII),\nB. Sbarufatti (PSU), M. H. Siegel (PSU) and A. Tohuvavohu (U Toronto)\nreport on behalf of the Neil Gehrels Swift Observatory Team:\n\nAt 23:32:06 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 211227A (trigger=1091101).  Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA, Dec 132.126, -2.702 which is \n   RA(J2000) = 08h 48m 30s\n   Dec(J2000) = -02d 42' 05\"\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 100 sec.  The peak count rate\nwas ~5200 counts/sec (15-350 keV), at ~1 sec after the trigger. \n\nThe XRT began observing the field at 23:33:20.3 UT, 73.5 seconds after\nthe BAT trigger. Using promptly downlinked data we find a bright,\nfading, uncatalogued X-ray source located at RA, Dec 132.14898,\n-2.73556 which is equivalent to:\n   RA(J2000)  = 08h 48m 35.76s\n   Dec(J2000) = -02d 44' 08.0\"\nwith an uncertainty of 3.8 arcseconds (radius, 90% containment). This\nlocation is 146 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 (2.37 x\n10^20 cm^-2, Willingale et al. 2013), with an excess column of 4.3\n(+3.24/-2.79) x 10^21 cm^-2 (90% confidence). \n\nThe initial flux in the 2.5 s image was 6.84e-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 81 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\n0.020. \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/)",
  "circularId": 31316,
  "createdOn": 1640648929000,
  "email": "palmer@lanl.gov",
  "subject": "GRB 211227A: Swift detection of a burst",
  "submitter": "David Palmer at LANL  <palmer@lanl.gov>",
  "eventId": "GRB 211227A"
}