{
  "bibcode": "2016GCN.20302....1D",
  "body": "V. D'Elia (ASDC), A. D'Ai (INAF-IASFPA), F. E. Marshall (NASA/GSFC),\nK. L. Page (U Leicester), T. Sakamoto (AGU),\nB. Sbarufatti (INAF-OAB/PSU) and T. N. Ukwatta (LANL) report on behalf\nof the Swift Team:\n\nAt 08:33:30 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 161220A (trigger=727610).  Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA, Dec 350.817, -47.502 which is \n   RA(J2000) = 23h 23m 16s\n   Dec(J2000) = -47d 30' 07\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The BAT light curve showed a FRED-like \nstructure with a duration of about 12 sec.  The peak count rate\nwas ~1285 counts/sec (15-350 keV), at ~1 sec after the trigger. \n\nThe XRT began observing the field at 08:34:39.2 UT, 69.1 seconds after\nthe BAT trigger. Using promptly downlinked data we find a bright,\nfading, uncatalogued X-ray source located at RA, Dec 350.84774,\n-47.49773, which is equivalent to:\n   RA(J2000)  = 23h 23m 23.46s\n   Dec(J2000) = -47d 29' 51.8\"\nwith an uncertainty of 3.7 arcseconds (radius, 90% containment). This\nlocation is 76 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 http://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 1.19\nx 10^20 cm^-2 (Willingale et al. 2013). \n\nThe initial flux in the 2.5 s image was 1.94e-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 78 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\n100% of the XRT error circle. The typical 3-sigma upper limit has been\nabout 19.6 mag. Results from the list of sources\ngenerated on-board are not available at this time. No correction has been made\nfor the expected extinction corresponding to E(B-V) of 0.01. \n\nBurst Advocate for this burst is V. D'Elia (delia AT asdc.asi.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/too.html.)",
  "circularId": 20302,
  "createdOn": 1482224200000,
  "email": "klp5@leicester.ac.uk",
  "subject": "GRB 161220A: Swift detection of a burst",
  "submitter": "Kim Page at U.of Leicester  <klp5@leicester.ac.uk>",
  "eventId": "GRB 161220A"
}