{
  "bibcode": "2013GCN.15151....1S",
  "body": "B. Sbarufatti (INAF-OAB/PSU), V. Mangano (PSU), M.C. Stroh (PSU), D.N.\nBurrows (PSU), C. Pagani (U. Leicester), A.P. Beardmore (U. Leicester),\nP.A. Evans (U. Leicester), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC) and\nL.M.Z. Hagen report on behalf of the Swift-XRT team:\n\nWe have analysed 6.2 ks of XRT data for GRB 130831A (Hagen  et al. GCN\nCirc. 15139),  from 115 s to 23.9 ks after the\tBAT trigger. The data\ncomprise 73 s in Windowed Timing (WT) mode (the first 10 s were taken\nwhile Swift was slewing) with the remainder in Photon Counting (PC)\nmode. The enhanced XRT position for this burst was given by Evans et\nal. (GCN. Circ 15147).\n\nThe light curve can be modelled with a series of power-law decays. The\ninitial decay index is alpha=3.0 (+0.4, -0.6). At T+239 s  the decay\nflattens to an alpha of -0.1 (+0.3, -0.6) before breaking again at\nT+783 s to a final decay with index alpha=1.09 (+0.09, -0.07).\n\nA spectrum formed from the WT mode data can be fitted with an absorbed\npower-law with a photon spectral index\tof 2.53 (+0.12, -0.11). The\nbest-fitting absorption column is  consistent with the Galactic value\nof 4.8 x 10^20 cm^-2 (Kalberla et al. 2005). The PC mode spectrum has a\nphoton index of 1.78 (+0.12, -0.08) and a best-fitting absorption\ncolumn of 5.2 (+2.8, -0.4) x 10^20 cm^-2. The counts to observed\n(unabsorbed) 0.3-10 keV flux conversion factor deduced from this\nspectrum  is 3.9 x 10^-11 (4.4 x 10^-11) erg cm^-2 count^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     5.2 (+2.8, -0.4) x 10^20 cm^-2\nGalactic foreground: 4.8 x 10^20 cm^-2\nExcess significance: <1.6 sigma\nPhoton index:\t     1.78 (+0.12, -0.08)\n\nIf the light curve continues to decay with a power-law decay index of\n1.09, the count rate at T+24 hours will be 0.024 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 9.5 x\n10^-13 (1.1 x 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/00568849.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 15151,
  "createdOn": 1377998463000,
  "email": "pae9@leicester.ac.uk",
  "subject": "GRB 130831A: Swift-XRT refined Analysis",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>",
  "eventId": "GRB 130831A"
}