{
  "bibcode": "2010GCN.11280....1L",
  "body": "O. M. Littlejohns (U Leicester) reports on behalf of the Swift-XRT team:\n\nWe have analysed 8.5 ks of XRT data for GRB 100915A (Littlejohns et al.\nGCN Circ. 11277), from 138 s to 18.8 ks after the BAT trigger. The data\ncomprise 95 s in Windowed Timing (WT) mode with the remainder in Photon\nCounting (PC) mode. The enhanced XRT position for this burst was given\nby Osborne et al. (GCN. Circ 11279).\n\nThe light curve can be modelled with a series of\npower-law decays. The initial decay index is alpha=0.9 (+0.6, -1.8). At\nT+320 s the decay steepens to an alpha of 2.4 (+0.6, -0.3). The light\ncurve breaks again at T+1058 s to a decay with alpha=0.66 (+0.16,\n-5.16), before a final break at T+6126 s after which the decay index is\n1.6 (+0.8, -0.3).\n\nA spectrum formed from the WT mode data can be fitted with an absorbed\npower-law with a photon spectral index of 1.37 (+0.21, -0.20). The\nbest-fitting absorption column is 3.8 (+1.3, -1.1) x 10^21 cm^-2, in\nexcess of the Galactic value of 2.3 x 10^21 cm^-2 (Kalberla et al.\n2005). The PC mode spectrum has a photon index of 1.74 (+/-0.18) and a\nbest-fitting absorption column of 4.6 (+1.0, -0.9) x 10^21 cm^-2. The\ncounts to observed (unabsorbed) 0.3-10 keV flux conversion factor\ndeduced from this spectrum is 5.5 x 10^-11 (8.2 x 10^-11) erg cm^-2\ncount^-1.\n\nIf the light curve continues to decay with a power-law decay index of\n1.6, the count rate at T+24 hours will be 1.1 x 10^-3 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.7 x\n10^-14 (8.4 x 10^-14) erg cm^-2 s^-1.\n\nThe results of the XRT-team automatic analysis are available at\nhttp://www.swift.ac.uk/xrt_products/00434178.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 11280,
  "createdOn": 1284550648000,
  "email": "oml2@star.le.ac.uk",
  "subject": "GRB 100915A: Swift-XRT refined analysis",
  "submitter": "Owen Littlejohns at U of Leicester  <oml2@star.le.ac.uk>",
  "eventId": "GRB 100915A"
}