{
  "bibcode": "2009GCN..9304....1E",
  "body": "P.A. Evans (U. Leicester) and C. B. Markwardt (CRESST/GSFC/UMD) report\non behalf of the Swift-XRT team:\n\nWe have analysed 6 ks of XRT data for GRB 090429A (Markwardt et al. GCN\nCirc. 9280). The first observation comprises a continuous observation\nfrom T0+64 s to T0+255 s  with the data  entirely in Windowed Timing\n(WT) mode. The second observation covers the range T0+35 to T0+64 ks,\nand contains 5.8 ks of Photon Counting (PC) mode data. The enhanced XRT\nposition for this burst was given by Evans et al. (GCN. Circ 9297).\n\nThe first observation shows a number of flares superimposed on a short,\ninitial rise which breaks at T0+100s to a power-law decay with index 2.7\n(+0.3, -0.2). The later PC mode data lie orders of magnitude above the\nextrapolation of this decay; the addition of a break around T0+1 ks to a\ndecay with power-law index 0.56 (+0.12, -0.06) produces a good fit to\nthe data. Due to the large observing gap the behaviour of the light\ncurve in the interval T0+255 s to T0+35 ks is unknown; if it is more\ncomplex than the simple behaviour we have modelled the final decay index\ncould differ significantly from the 0.56 (+0.12, -0.06) value we obtained.\n\nA spectrum formed from the PC mode data can be fitted with an absorbed\npower-law with a photon spectral index of 2.0 (+1.0, -0.7). The\nbest-fitting absorption column is 1.20 (+2.36, -0.77) x 10^21 cm^-2,\nconsistent with the Galactic value of 4.2 x 10^20 cm^-2 (Kalberla et al.\n2005). The counts to observed (unabsorbed) 0.3-10 keV flux conversion\nfactor deduced from this spectrum is 3.8 x 10^-11 (5.0 x 10^-11) erg\ncm^-2 count^-1.\n\nIf the light curve continues to decay with a power-law decay index of\n0.56, the count rate at T+48 hours will be 5.9 x 10^-3 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.2 x\n10^-13 (2.9 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/00350853.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 9304,
  "createdOn": 1241087980000,
  "email": "pae9@star.le.ac.uk",
  "subject": "GRB 090429A: Swift-XRT refined analysis",
  "submitter": "Phil Evans at U of Leicester  <pae9@star.le.ac.uk>",
  "eventId": "GRB 090429A"
}