{
  "bibcode": "2009GCN..9881....1D",
  "body": "V. D'Elia (ASDC), S. D. Barthelmy (GSFC),\nW. H. Baumgartner (GSFC/UMBC), D. N. Burrows (PSU),\nJ. R. Cummings (NASA/UMBC), S. T. Holland (CRESST/USRA/GSFC),\nJ. A. Kennea (PSU), C. B. Markwardt (CRESST/GSFC/UMD),\nF. E. Marshall (NASA/GSFC), C. Pagani (PSU), M. Perri (ASDC),\nM. H. Siegel (PSU), M. Stamatikos (OSU/NASA/GSFC), M. A. Stark (PSU)\nand T. N. Ukwatta (GSFC/GWU) report on behalf of the Swift Team:\n\nAt 01:24:18 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 090904B (trigger=361831).  Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA, Dec 264.191, -25.212 which is \n   RA(J2000)  =  17h 36m 46s\n   Dec(J2000) = -25d 12' 43\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The BAT light curve shows multiple overlapping peaks\nstarting at T-5 sec with a duration of about 60 sec.  The peak count rate\nwas ~1800 counts/sec (15-350 keV), at ~3 sec after the trigger. \n\nThe XRT began observing the field at 01:26:32.3 UT, 134.2 seconds after\nthe BAT trigger. Using promptly downlinked data we find an uncatalogued\nX-ray source with an enhanced position: RA, Dec 264.1854, -25.2138\nwhich is equivalent to:\n   RA(J2000)  = 17h 36m 44.50s\n   Dec(J2000) = -25d 12' 49.7\"\nwith an uncertainty of 2.4 arcseconds (radius, 90% containment). This\nlocation is 19 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. \n\nA power-law fit to a spectrum formed from promptly downlinked event\ndata gives a column density in excess of the Galactic value (3.28e+21\ncm^-2, Kalberla et al. 2005), with an excess column of 4.8\n(+5.33/-4.01) x 10^21 cm^-2 (90% confidence). \n\nUVOT took a finding chart exposure of 150 seconds with the White\nfilter  starting 137 seconds after the BAT trigger. No credible\nafterglow candidate has  been found in the initial data products. The\n2.7'x2.7' sub-image covers 100% of the XRT error circle. The 8'x8'\nregion for the list of sources generated on-board covers 100% of the\nXRT error circle.  Because of the density of catalogued stars,further\nanalysis is required to report an upper limit for any afterglow in the\nregion. \n\nWe note that this is a separate burst from the \"A\" burst.  \nBut there may be some confusion resulting from overlapping GCN Notices. \n\nBurst Advocate for this burst is V. D'Elia (delia 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": 9881,
  "createdOn": 1252029016000,
  "email": "scott@lheamail.gsfc.nasa.gov",
  "subject": "GRB 090904B: Swift detection of a burst",
  "submitter": "Scott Barthelmy at NASA/GSFC  <scott@lheamail.gsfc.nasa.gov>",
  "eventId": "GRB 090904B"
}