{
  "bibcode": "2018GCN.22994....1S",
  "body": "B. Sbarufatti (PSU), F. E. Marshall (NASA/GSFC) and\nD. M. Palmer (LANL) report on behalf of the Neil Gehrels Swift\nObservatory Team:\n\nAt 11:06:48 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 180721A (trigger=849018).  Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA, Dec 347.695, +4.880 which is \n   RA(J2000) = 23h 10m 47s\n   Dec(J2000) = +04d 52' 47\"\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 60 sec.  The peak count rate\nwas ~1800 counts/sec (15-350 keV), at ~0 sec after the trigger. \n\nThe XRT began observing the field at 11:07:45.3 UT, 56.9 seconds after\nthe BAT trigger. Using promptly downlinked data we find a bright,\nfading, uncatalogued X-ray source with an enhanced position: RA, Dec\n347.7100, 4.8553 which is equivalent to:\n   RA(J2000)  = 23h 10m 50.41s\n   Dec(J2000) = +04d 51' 19.1\"\nwith an uncertainty of 2.3 arcseconds (radius, 90% containment). This\nlocation is 103 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\nhttp://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 (6.47 x\n10^20 cm^-2, Willingale et al. 2013), with an excess column of 3.7\n(+3.22/-2.74) x 10^21 cm^-2 (90% confidence). \n\nThe initial flux in the 2.5 s image was 7.38e-10 erg cm^-2 s^-1 (0.2-10\nkeV). \n\nUVOT took a finding chart exposure of 250 seconds with the U filter starting\n119 seconds after the BAT trigger. No credible afterglow candidate has been\nfound in the initial data products. The 2.7'x2.7' sub-image covers 100% of the\nXRT error circle. The typical 3-sigma upper limit has been about 19.2 mag. The\n8'x8' region for the list of sources generated on-board covers 100% of the XRT\nerror circle. The list of sources is typically complete to about 18.0 mag. No\ncorrection has been made for the expected extinction corresponding to E(B-V) of\n0.07. \n\nBurst Advocate for this burst is B. Sbarufatti (bxs60 AT 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": 22994,
  "createdOn": 1532172041000,
  "email": "palmer@lanl.gov",
  "subject": "GRB 180721A: Swift detection of a burst",
  "submitter": "David Palmer at LANL  <palmer@lanl.gov>",
  "eventId": "GRB 180721A"
}