{
  "bibcode": "2009GCN..9790....1B",
  "body": "A. P. Beardmore (U. Leicester) and J. R. Cummings (NASA/UMBC) report\non behalf of the Swift-XRT team:\n\nWe have analysed 8.8 ks of XRT data for GRB 090813 (Cummings et\nal., GCN Circ. 9781), from 84 s to 19.3 ks after the BAT trigger. The\ndata span four orbits, comprising 810 s in Windowed Timing (WT) mode\nwith the remainder in Photon Counting (PC) mode. The enhanced XRT\nposition for this burst was given by Osborne et al. (GCN. Circ 9785).\n\nThe X-ray light curve initially follows a shallow decay, with a decay \nindex of 0.22 +/ 0.10, before steepening to an index of 1.15 +/- 0.03 at \nabout 450 s after the trigger.\n\nA spectrum formed from the WT mode data can be fitted with an absorbed\npower-law with a photon spectral index of 2.10 +/- 0.07. The\nbest-fitting absorption column is (2.23 +0.20 -0.19) x 10^21 cm^-2, in\nexcess of the Galactic value of 6.3 x 10^20 cm^-2 (Kalberla et al.\n2005). The PC mode spectrum has a photon index of 2.00 +0.11 -0.10 and\na best-fitting absorption column of (2.3 +/- 0.3) x 10^21 cm^-2. The\ncounts to observed (unabsorbed) 0.3-10 keV flux conversion factor\ndeduced from this spectrum is 4.3 x 10^-11 (6.4 x 10^-11) erg cm^-2\ncount^-1.\n\nIf the light curve continues to decay with a power-law decay index of\n1.15, the estimated count rate at T+24 hours will be 0.016 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of\n6.9 x 10^-13 (1.0x 10^-12) erg cm^-2 s^-1.\n\nThe results of the XRT-team automatic analysis are available at\nhttp://www.swift.ac.uk/xrt_products/00359884.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 9790,
  "createdOn": 1250178236000,
  "email": "apb@star.le.ac.uk",
  "subject": "GRB 090813: Swift-XRT refined analysis",
  "submitter": "Andy Beardmore at U Leicester  <apb@star.le.ac.uk>",
  "eventId": "GRB 090813"
}