{
  "bibcode": "2016GCN.19833....1S",
  "body": "M. H. Siegel (PSU), S. D. Barthelmy (GSFC), D. N. Burrows (PSU),\nA. Y. Lien (GSFC/UMBC), F. E. Marshall (NASA/GSFC),\nD. M. Palmer (LANL) and B. Sbarufatti (INAF-OAB/PSU) report on behalf\nof the Swift Team:\n\nAt 22:29:13 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 160821B (trigger=709357).  Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA, Dec 279.987, +62.393, which is \n   RA(J2000)  =  18h 39m 57s\n   Dec(J2000) = +62d 23' 34\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The BAT light curve shows a single spike\nstructure with a duration of about 0.5 sec.  The peak count rate\nwas ~5000 counts/sec (15-350 keV), at ~0 sec after the trigger. \n\nThe XRT began observing the field at 22:30:19.1 UT, 66.0 seconds after\nthe BAT trigger. Using promptly downlinked data we find a bright,\nfading, uncatalogued X-ray source with an enhanced position: RA, Dec\n279.9780, 62.3920 which is equivalent to:\n   RA(J2000)  = 18h 39m 54.71s\n   Dec(J2000) = +62d 23' 31.3\"\nwith an uncertainty of 2.5 arcseconds (radius, 90% containment). This\nlocation is 15 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 5.75\nx 10^20 cm^-2 (Willingale et al. 2013). \n\nThe initial flux in the 2.5 s image was 1.45e-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 76 seconds after the BAT trigger. No credible afterglow candidate has\nbeen found in the initial data products. The 2.7'x2.7' covers 100% of\nthe XRT error region. The typical 3-sigma upper limit has\nbeen about 19.6 mag. No correction has been made\nfor the expected extinction corresponding to E(B-V) of 0.05. \n\nBurst Advocate for this burst is M. H. Siegel (siegel AT swift.psu.edu). \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": 19833,
  "createdOn": 1471819432000,
  "email": "scott@milkyway.gsfc.nasa.gov",
  "subject": "GRB 160821B: Swift detection of a short burst",
  "submitter": "Scott Barthelmy at NASA/GSFC  <scott@milkyway.gsfc.nasa.gov>",
  "eventId": "GRB 160821B"
}