{
  "bibcode": "2009GCN..9750....1M",
  "body": "R. Margutti (Univ. Bicocca & INAF-OAB), J. Mao (INAF-OAB),\nA. de Ugarte Postigo (INAF-OAB)  and J. K. Cannizzo (NASA/UMBC)\nreport on behalf of the Swift-XRT team:\n\nWe have analysed the first orbit of Swift-XRT data obtained for\nGRB 090807 (Cannizzo et al. GCN Circ. 9746), covering 149 s of\nWindowed Timing (WT) and 1.5 ks of Photon Counting (PC) mode data,\nrespectively, between 154 s and 1.9 ks after the trigger.\nThe UVOT-enhanced XRT position was given by Beardmore et al. in\nGCN Circ. 9748.\n\nThe light curve shows a large flare peaking around 185 s which was\nalso detected in the 15-150 keV energy range by Swift/BAT (Ukwatta et\nal. GCN Circ. 9749). The underlying light curve decays\nwith a power-law index of 5.0 +/- 0.5. Around T+580 s the decay flattens,\nto a slope of 0.87 +/- 0.42.\n\nThe spectrum extracted from WT data can be modelled with an absorbed simple\npower-law, with Gamma = 2.2 +/- 0.1 and NH = (3.0+/-0.2)x10^21 cm^-2 in\nexcess of the Galactic column in this direction which is 8.6x10^20 cm^-2\n(Kalberla et al. 2005).\nA spectrum extracted from PC data in the time interval T+310 s - T+1840 s\nhas a best-fitting photon index of 2.6 +/- 0.4 and a best-fitting \nabsorption\ncolumn of NH = (3.3+/-0.1)x10^21 cm^-2 in excess of the Galactic value.\nThe counts to observed (unabsorbed) 0.3-10 keV flux conversion factor\ndeduced from this spectrum is 3.1 x 10^-11 (8.4 x 10^-11) erg cm^-2 \ncount^-1.\n\nIf the light curve continues to decay with a power-law decay index\nof 0.9, the count rate at T+24 hours will be 0.002 count s^-1, \ncorresponding\nto an observed (unabsorbed) 0.3-10 keV flux of 6.2 x 10^-14 (1.7 x 10^-13)\nerg cm^-2 s^-1. However, the light-curve is possible to break before \nthis time,\nmaking this prediction unreliable.\n\nThe results of the XRT-team automatic analysis are available at\nhttp://www.swift.ac.uk/xrt_products/00359378.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 9750,
  "createdOn": 1249684624000,
  "email": "raffaella.margutti@brera.inaf.it",
  "subject": "GRB 090807: Swift-XRT refined analysis",
  "submitter": "Raffaella Margutti at U. di Milano Bicocca  <raffaella.margutti@brera.inaf.it>",
  "eventId": "GRB 090807"
}