{
  "bibcode": "2006GCN..5505....1G",
  "body": "D. Grupe (PSU), S. D. Barthelmy (GSFC), M. M. Chester (PSU),\nJ. R. Cummings (NASA/UMD), S. T. Holland (GSFC/USRA),\nS. D. Hunsberger (PSU), J. A. Kennea (PSU), H. A. Krimm (GSFC/USRA),\nC. B. Markwardt (GSFC/UMD), F. E. Marshall (NASA/GSFC),\nD. M. Palmer (LANL), M. Stamatikos (NASA/ORAU) and M. C. Stroh (PSU)\nreport on behalf of the Swift Team:\n\nAt 02:31:03 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 060904B (trigger=228006).  Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA,Dec 58.213, -0.720 {03h 52m 51s, -00d 43' 11\"} (J2000)\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The BAT light curve shows an initial 5-sec wide\npeak at T+1 sec followed by an ~30-sec wide weaker peak at T+150 sec. \nThe total duration is about 180 sec.  The peak count rate\nwas ~3000 counts/sec (15-350 keV), at ~1 sec after the trigger. \n\nThe XRT began observing the field at 02:32:12 UT, 69 seconds after the\nBAT trigger. XRT found a variable, uncatalogued X-ray source located\nat RA(J2000) = 03h 52m 50.0s, Dec(J2000) = -00d 43' 32.8\", with an\nestimated uncertainty of 6.5 arcseconds (90% confidence radius). This\nlocation is 26 arcseconds from the BAT on-board position, within the\nBAT error circle. The initial flux in the 2.5s image was 4.3e-10\nerg/cm2/s (0.2-10 keV). The source shows a rapid increase in count\nrate indicating a bright flare that is possibly correlated with the \nsecond bright peak in the BAT. \n\nUVOT took a finding chart exposure of 246 seconds with the V filter\nstarting 70 seconds after the BAT trigger. There is a candidate afterglow in the\nrapidly available 2.7'x2.7' sub-image at (RA,DEC) (J2000) of\n(58.2106,-0.7253) or (03h52m50.54s,-00o43'31.1\")  with a 1-sigma\nerror radius of about 0.7 arc sec. This position is 7.7 arc sec. from\nthe center of the XRT error circle. The estimated magnitude is 18.6\nwith a 1-sigma error of about 0.5 mag. No correction has been made\nfor the expected extinction of about 0.6 magnitudes.",
  "circularId": 5505,
  "createdOn": 1157338283000,
  "email": "scott@lheamail.gsfc.nasa.gov",
  "subject": "GRB 060904B: Swift detection of a burst with optical counterpart",
  "submitter": "Scott Barthelmy at NASA/GSFC  <scott@lheamail.gsfc.nasa.gov>",
  "eventId": "GRB 060904B"
}