{
  "bibcode": "2019GCN.26534....1L",
  "body": "S Laha (GSFC/UMBC/CRESST), S. D. Barthelmy (GSFC), J.D. Gropp (PSU),\nJ. A. Kennea (PSU), N. P. M. Kuin (UCL-MSSL), A. Y. Lien (GSFC/UMBC),\nF. E. Marshall (NASA/GSFC), K. L. Page (U Leicester) and\nK. K. Simpson (PSU) report on behalf of the Neil Gehrels Swift\nObservatory Team:\n\nAt 20:39:13 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 191221B (trigger=945521).  Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA, Dec 154.832, -38.141 which is \n   RA(J2000) = 10h 19m 20s\n   Dec(J2000) = -38d 08' 28\"\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 15 sec.  The peak count rate\nwas ~17000 counts/sec (15-350 keV), at ~5 sec after the trigger. \n\nThe XRT began observing the field at 20:40:39.3 UT, 86.2 seconds after\nthe BAT trigger. XRT found a bright, uncatalogued X-ray source located\nat RA, Dec 154.8286, -38.1579 which is equivalent to:\n   RA(J2000)  = 10h 19m 18.86s\n   Dec(J2000) = -38d 09' 28.4\"\nwith an uncertainty of 6.8 arcseconds (radius, 90% containment). This\nlocation is 61 arcseconds from the BAT onboard position, within the BAT\nerror circle. No event data are yet available to determine the column\ndensity using X-ray spectroscopy. \n\nUVOT took a finding chart exposure of 150 seconds with the White filter\nstarting 91 seconds after the BAT trigger. A very bright afterglow candidate has\nbeen found at the XRT position in the initial data products. Because of \ncoincidence loss we cannot calculate the magnitude accurately at this time. \nNo correction has been made for the expected extinction corresponding to E(B-V) of 0.08. \n\nBurst Advocate for this burst is S Laha (sib.laha 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/)",
  "circularId": 26534,
  "createdOn": 1576962024000,
  "email": "sib.laha@gmail.com",
  "subject": "GRB 191221B: Swift detection of a burst and a very bright optical candidate",
  "submitter": "Sibasish Laha at GSFC  <sib.laha@gmail.com>",
  "eventId": "GRB 191221B"
}