{
  "bibcode": "2009GCN..9894....1P",
  "body": "M. Perri, V. D'Elia, G. Stratta (ASDC) report on behalf of the\nSwift-XRT team:\n\nWe have analysed the first 12 ks of XRT data for GRB 090904A (Perri et\nal.,\nGCN Circ. 9879), from 134 s to 29.6 ks after the BAT trigger. The enhanced\nXRT position for this burst was given by Evans (GCN. Circ. 9891).\n\nDuring the first Swift orbit, the light-curve shows a steep decay\nwith a large superimposed flare peaking at about T+300 s. Starting\nfrom T+1000 s, the curve is well described by a broken power-law model\nwith temporal decay indices alpha1=0.2+/-0.1, alpha2=0.9+/-0.3 and a\ntemporal break at around T+12 ks.\n\nA spectrum extracted from the PC mode data from T+460 s to T+29.6 ks can\nbe fitted with an absorbed power-law model with a photon spectral index of\n2.46 (+0.16,-0.26) and an absorption column density of\n1.03 (+0.66,-0.64)e21 cm-2 in excess of the Galactic value of\n9.3e20 cm-2 (Kalberla et al. 2005). The counts-to-observed (-unabsorbed)\n0.3-10 keV flux conversion factor deduced from this spectrum is\n3.3e-11 (6.2e-11) erg cm-2 count-1. Errors are given at the\n90% confidence level.\n\nIf the light curve continues to decay with a power-law index of\n0.9, the count rate at T+24 hours will be 6e-3 count s-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of\n2.0e-13 (3.7e-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/00361830.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 9894,
  "createdOn": 1252083363000,
  "email": "perri@asdc.asi.it",
  "subject": "GRB 090904A: Swift-XRT refined analysis",
  "submitter": "Matteo Perri at ISAC/ASDC  <perri@asdc.asi.it>",
  "eventId": "GRB 090904A"
}