{
  "bibcode": "2009GCN..9893....1D",
  "body": "V. D'Elia, G. Stratta, M. Perri (ASDC) report on behalf of\nthe Swift-XRT team:\n\nWe have analysed 6.2 ks of XRT data for GRB 090904B (D'Elia et al. GCN\nCirc. 9881), from 159 s to 37.1 ks after the BAT trigger. The data are\nentirely in Photon Counting (PC) mode. The enhanced XRT position for\nthis burst was given by Osborne et al. (GCN. Circ 9987).\n\nThe light curve, after an initial rise, peaks at T+260 s, while the \nfollowing\ndecay can be modelled with a power-law with a decay\nindex of alpha=1.20+-0.05 (90% confidence level).\n\nA spectrum formed from the PC mode data can be fitted with an absorbed\npower-law with a photon spectral index of 1.67 (+0.26, -0.24, 90%\nconfidence level). The best-fitting absorption column is 6.3\n(+2.5, -1.1) x 1021 cm-2, in excess with respect to the Galactic value of\n3.3 x 1021 cm-2 (Kalberla et al. 2005). The counts to observed\n(unabsorbed) 0.3-10 keV flux conversion factor deduced from this\nspectrum is 6.8 x 10-11 (1.1 x 10-10) erg cm-2 count-1.\n\nIf the light curve continues to decay with a power-law decay index of\n1.20, the count rate at T+24 hours will be 0.0040 count s-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.7 x\n10-13 (4.4 x 10-13) erg cm-2 s-1.\n\nThe results of the XRT-team automatic analysis are available at\nhttp://www.swift.ac.uk/xrt_products/00361831.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 9893,
  "createdOn": 1252082947000,
  "email": "delia@mporzio.astro.it",
  "subject": "GRB 090904B: Swift XRT Refined Analysis",
  "submitter": "Valerio D'Elia at INAF-OAR  <delia@mporzio.astro.it>",
  "eventId": "GRB 090904B"
}