{
  "bibcode": "2008GCN..8506....1B",
  "body": "A.P. Beardmore, K.L. Page (U. Leicester) and S. Immler (CRESST/GSFC/UMD) \nreport on behalf of the Swift-XRT team.\n\nThe Swift-XRT started observing the field of GRB 081109A (trigger\n#334112, Immler et al., GCN 8500) at 07:03:12.2 UT, 65.6 s after\nthe BAT trigger. The XRT observed the GRB in Windowed Timing (WT) mode \nuntil 318 s after the trigger and Photon Counting (PC) mode thereafter.\n\nUsing 4661 s of XRT Photon Counting mode data and 7 UVOT images, we\nfind an astrometrically corrected X-ray position (using the XRT-UVOT\nalignment and matching to the USNO-B1 catalogue) of\nRA, Dec = 330.7905, -54.7118 which is equivalent to :\n\nRA  (J2000):  22h 03m 9.72s\nDec (J2000): -54d 42m 42.5s\n\nwith an uncertainty of 1.4 arcsec (90% confidence).  This is 2.98\narcsec from the reported possible NIR counterpart of D'Avanzo (GCN\n8501).\n\nThe X-ray light curve from the first three orbits can be modelled with\na broken powerlaw with an initial decay slope of 1.78 +/- 0.06, a break \ntime of 353 +/- 40 s, followed by a shallower decay slope of 0.99 +/- 0.04.\n\nThe spectrum of the WT data from orbit 1 (from T+71.9 s to T+318.4 s, \nwhere T is the trigger time) can be well fit by an absorbed powerlaw \nwith a photon index of 1.72 +/- 0.08 and column density of \n(1.84 +/- 0.22) x 10^21 cm^-2, compared with the Galactic column \ndensity of 1.6 x 10^20 cm^-2 in the direction of the burst. The observed\n0.3-10 keV flux is  (7.4 +/- 0.4) x 10^-10 erg cm^-2 s^-1. The \ncorresponding unabsorbed 0.3-10 keV flux is (9.5 +/- 0.5) x 10^-10 \nerg cm^-2 s^-1.\n\nA powerlaw fit to a  spectrum  obtained from  PC mode data spanning \norbits 2 to 3 (T+4.76 ks to T+12.88 ks) is best fit with a photon \nindex of   2.20 +/- 0.20 and column density (3.1 +/- 0.7) x 10^21 cm^-2.\nThe observed 0.3-10 keV flux over this interval is (7.3 +/- 0.7) x 10^-12\nerg cm^-2 s^-1. The  count-to-observed-flux conversion factor is \n6.0e-11 erg cm^-2 count^-1.\n\nAssuming the X-ray emission from the burst continues to decline at the\nsame rate we predict an XRT count rate of 0.018 count s^-1 at T+24 hour, \nor an observed 0.3-10 keV X-ray flux of 1.1 x 10^-12 erg cm^-2 s^-1.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 8506,
  "createdOn": 1226247547000,
  "email": "apb@star.le.ac.uk",
  "subject": "GRB 081109A: Swift-XRT refined analysis",
  "submitter": "Andy Beardmore at U Leicester  <apb@star.le.ac.uk>",
  "eventId": "GRB 081109A"
}