{
  "bibcode": "2018GCN.22589....1G",
  "body": "J.D. Gropp (PSU), D. N. Burrows (PSU), A. Deich (PSU),\nC. Gronwall (PSU), J. A. Kennea (PSU), A. Y. Lien (GSFC/UMBC),\nF. E. Marshall (NASA/GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU) and\nM. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift\nObservatory Team:\n\nAt 00:45:35 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 180404A (trigger=821881).  Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA, Dec 83.564, -37.170 which is \n   RA(J2000) = 05h 34m 15s\n   Dec(J2000) = -37d 10' 10\"\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 50 sec.  The peak count rate\nwas ~1900 counts/sec (15-350 keV), at ~0 sec after the trigger. \n\nThe XRT began observing the field at 00:47:02.1 UT, 86.5 seconds after\nthe BAT trigger. Using promptly downlinked data we find an uncatalogued\nX-ray source located at RA, Dec 83.54900, -37.16824 which is equivalent\nto:\n   RA(J2000)  = 05h 34m 11.76s\n   Dec(J2000) = -37d 10' 05.7\"\nwith an uncertainty of 4.2 arcseconds (radius, 90% containment). This\nlocation is 43 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.  We\ncannot determine whether the source is fading at the present time. No\nspectrum from the promptly downlinked event data is yet available to\ndetermine the column density. \n\nUVOT took a finding chart exposure of 150 seconds with the White filter\nstarting 89 seconds after the BAT trigger. There is a candidate afterglow in\nthe rapidly available 2.7'x2.7' sub-image at\n  RA(J2000)  =\t05:34:11.63 =  83.54846\n  DEC(J2000) = -37:10:03.9  = -37.16774\nwith a 90%-confidence error radius of about 0.65 arc sec. This position is 2.3\narc sec. from the center of the XRT error circle. The estimated magnitude is\n19.40 with a 1-sigma error of about  0.16. No correction has been made for the\nexpected extinction corresponding to E(B-V) of 0.04. \n\nBurst Advocate for this burst is J.D. Gropp (jdg44 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": 22589,
  "createdOn": 1522803292000,
  "email": "palmer@lanl.gov",
  "subject": "GRB 180404A: Swift detection of a burst with an optical afterglow",
  "submitter": "David Palmer at LANL  <palmer@lanl.gov>",
  "eventId": "GRB 180404A"
}