{
  "bibcode": "2009GCN..9754....1M",
  "body": "C. B. Markwardt (CRESST/GSFC/UMD), S. D. Barthelmy (GSFC),\nM. M. Chester (PSU), A. de Ugarte Postigo (INAF-OAB),\nN. Gehrels (NASA/GSFC), C. Guidorzi (U Ferrara),\nS. T. Holland (CRESST/USRA/GSFC), J. A. Kennea (PSU),\nN. P. M. Kuin (MSSL), W.B Landsman (GSFC), J. Mao (INAF-OAB),\nR. Margutti (Univ Bicocca&OAB), P. T. O'Brien (U Leicester),\nK. L. Page (U Leicester), P. Romano (INAF-IASFPA) and\nM. H. Siegel (PSU) report on behalf of the Swift Team:\n\nAt 17:31:14 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 090809 (trigger=359530).  Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA, Dec 328.645, -0.083 which is \n   RA(J2000)  =  21h 54m 35s\n   Dec(J2000) = -00d 04' 59\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The BAT light curve shows a weak peak\nwith a duration of about 10 sec.  The peak count rate\nwas ~900 counts/sec (15-350 keV), at ~1 sec after the trigger. \n\nThe XRT began observing the field at 17:32:58.5 UT, 104.0 seconds after\nthe BAT trigger. Using promptly downlinked data we find an uncatalogued\nX-ray source located at RA, Dec 328.67772, -0.08465 which is equivalent\nto:\n   RA(J2000)  = 21h 54m 42.65s\n   Dec(J2000) = -00d 05' 04.7\"\nwith an uncertainty of 4.5 arcseconds (radius, 90% containment). This\nlocation is 117 arcseconds from the BAT onboard position, within the\nBAT error circle. This position may be improved as more data are\nreceived; the latest position is available at\nhttp://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 (6.08e+20\ncm^-2, Kalberla et al. 2005), with an excess column of 2.5\n(+2.71/-2.28) x 10^21 cm^-2 (90% confidence). \n\nUVOT took a finding chart exposure of  86 seconds with the White \nfilter  starting 107 seconds after the BAT trigger. A possible \nafterglow candidate has  been found in the list of sources generated \non-board, located at RA=328.68008  (21:54:43.22), dec=-0.08385 \n(-00:05:01.9), with an estimated White magnitude = 19.9 +/-0.4.  The \n2.7'x2.7' sub-image does not include the XRT position. No  correction \nhas been made for the expected extinction corresponding to E(B-V) of  \n0.10. \n\nBurst Advocate for this burst is C. B. Markwardt (Craig.Markwardt AT nasa.gov). \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": 9754,
  "createdOn": 1249840290000,
  "email": "scott@lheamail.gsfc.nasa.gov",
  "subject": "GRB 090809: Swift detection of a burst with a possible optical counterpart",
  "submitter": "Scott Barthelmy at NASA/GSFC  <scott@lheamail.gsfc.nasa.gov>",
  "eventId": "GRB 090809"
}