{
  "bibcode": "2018GCN.22590....1L",
  "body": "S. J. LaPorte (PSU), C. Gronwall (PSU), J.D. Gropp (PSU),\nJ. A. Kennea (PSU), A. Y. Lien (GSFC/UMBC),\nF. E. Marshall (NASA/GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU) and\nA. Tohuvavohu (PSU) report on behalf of the Neil Gehrels Swift\nObservatory Team:\n\nAt 02:11:44 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 180404B (trigger=821902).  Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA, Dec 53.384, -50.195 which is \n   RA(J2000) = 03h 33m 32s\n   Dec(J2000) = -50d 11' 41\"\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 50 sec.  The peak count rate\nwas ~9000 counts/sec (15-350 keV), at ~9 sec after the trigger. \n\nThe XRT began observing the field at 02:12:53.9 UT, 69.9 seconds after\nthe BAT trigger. XRT found a bright, uncatalogued X-ray source located\nat RA, Dec 53.3967, -50.2151 which is equivalent to:\n   RA(J2000)  = +03h 33m 35.21s\n   Dec(J2000) = -50d 12' 54.4\"\nwith an uncertainty of 4.7 arcseconds (radius, 90% containment). This\nlocation is 78 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 81 seconds after the BAT trigger. There is a candidate afterglow in\nthe rapidly available 2.7'x2.7' sub-image at\n  RA(J2000)  =\t03:33:34.24 =  53.39265\n  DEC(J2000) = -50:12:54.1  = -50.21504\nwith a 90%-confidence error radius of about 0.76 arc sec. This position is 9.3\narc sec. from the center of the XRT error circle. The estimated magnitude is\n18.61 with a 1-sigma error of about  0.15. No correction has been made for the\nexpected extinction corresponding to E(B-V) of 0.01. \n\nBurst Advocate for this burst is S. J. LaPorte (extragsam 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/too.html.)",
  "circularId": 22590,
  "createdOn": 1522808636000,
  "email": "palmer@lanl.gov",
  "subject": "GRB 180404B: Swift detection of a burst with an optical counterpart",
  "submitter": "David Palmer at LANL  <palmer@lanl.gov>",
  "eventId": "GRB 180404B"
}