{
  "bibcode": "2009GCN.10055....1S",
  "body": "G. Stratta (ASDC) reports on behalf of the Swift-XRT team:\n\nThe Swift-XRT began observing GRB 091018 (trigger=373172) on\n2009-10-18 at 20:49:20.5 UT, 60.9 seconds after the BAT trigger\n(Stamatikos et al., GCN Circ. 7226). The data have been\ntaken in Windowed Timing (WT) mode from T + 67 s to T + 144 s\nand in Photon Counting (PC) mode later on.\n\nEnhanced position of the detected, bright X-ray afterglow\nwas given by Osborne et al. (GCN Circ. 10037)\n\nThe X-ray light curve from T + 67 s to T + 53.3 ks is well\nfit by a broken power law model (chi^2 = 115 for 128 degrees\nof freedom) with a temporal break at tb = T + (500 +/- 100) s and\ndecay indices alpha1 = -0.4 +/- 0.1 and alpha2 = -1.17 +/- 0.03\nbefore and after the break, respectively.\n\nThe 0.3-10 keV spectrum from T + 156 s to T + 7.1 ks\nis well fit by an absorbed power law (reduced chi2 of 1.0, with\n50 degrees of freedom). The best fit photon index is 1.9 +/- 0.1,\nwith an hydrogen column density at the burst rest frame\n(z=0.971, Hsiao-Wen Chen et al. GCN Circ.10038) of\nNHz = (1.4 +/- 0.8)e21 cm^-2 in addition to the Galactic column\nalong the line of sight, that is NH = 2.8e20 cm^-2\n(Kalberla et al. 2005). Errors are given at 90% confidence level.\nThe observed (unabsorbed) flux in the 0.3-10 keV band is\n1.5(1.8)e-10 erg cm^-2 s^-1.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 10055,
  "createdOn": 1256126155000,
  "email": "giulia.stratta@gmail.com",
  "subject": "GRB 091018: Swift XRT refined analysis",
  "submitter": "Giulia Stratta at ASDC  <giulia.stratta@gmail.com>",
  "eventId": "GRB 091018"
}