{
  "bibcode": "2009GCN..9879....1P",
  "body": "M. Perri (ASDC), S. D. Barthelmy (GSFC),\nW. H. Baumgartner (GSFC/UMBC), D. N. Burrows (PSU), V. D'Elia (ASDC),\nS. T. Holland (CRESST/USRA/GSFC), J. A. Kennea (PSU),\nF. E. Marshall (NASA/GSFC), M. H. Siegel (PSU),\nM. Stamatikos (OSU/NASA/GSFC), M. A. Stark (PSU) and\nT. N. Ukwatta (GSFC/GWU) report on behalf of the Swift Team:\n\nAt 01:01:06 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 090904 (trigger=361830).  Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA, Dec 100.882, +50.206 which is \n   RA(J2000) = 06h 43m 32s\n   Dec(J2000) = +50d 12' 23\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The BAT light curve shows a small peak at T_zero\nand then two large peaks at T+130 and T+175 sec with a duration\nof at least 200 sec.  The peak count rate\nwas ~2500 counts/sec (15-350 keV), at ~T+130 sec after the trigger. \n\nThe XRT began observing the field at 01:05:38.6 UT, 271.7 seconds after\nthe BAT trigger. XRT found a bright, uncatalogued, fading X-ray source located\nat RA, Dec 100.8816, +50.2040 which is equivalent to:\n   RA(J2000)  = 06h 43m 31.58s\n   Dec(J2000) = +50d 12' 14.4\"\nwith an uncertainty of 5.2 arcseconds (radius, 90% containment). This\nlocation is 7.3 arcseconds from the BAT onboard position, within the\nBAT error circle. No event data are yet available to determine the\ncolumn density using X-ray spectroscopy. \n\nThe XRT prompt light curve shows a large flare peaking about 30s \nafter the start of the XRT observations. \n\nThe initial flux in the 2.5 s image was 1.71e-09 erg cm^-2 s^-1 (0.2-10\nkeV). \n\n\nUVOT took a finding chart exposure of 150 seconds with the White filter\nstarting 141 seconds after the BAT trigger. No credible afterglow candidate has\nbeen found in the initial data products. Because part of the 2.7'x2.7'\nsub-image was not received, the overlap with the XRT error circle is uncertain. \nThe 8'x8' region for the list of sources generated on-board covers 100% of the\nXRT error circle. The list of sources is typically complete to about 18 mag. No\ncorrection has been made for the expected extinction corresponding to E(B-V) of\n0.10. \n\n\n\n\nBurst Advocate for this burst is M. Perri (perri AT asdc.asi.it). \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": 9879,
  "createdOn": 1252027085000,
  "email": "scott@lheamail.gsfc.nasa.gov",
  "subject": "GRB 090904: Swift detection of a burst",
  "submitter": "Scott Barthelmy at NASA/GSFC  <scott@lheamail.gsfc.nasa.gov>",
  "eventId": "GRB 090904"
}