{
  "bibcode": "2015GCN.18147....1B",
  "body": "A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), B.P. Gompertz\n(U. Leicester), P. D'Avanzo (INAF-OAB), A. D'ai (INAF-IASFPA), T.G.R.\nRoegiers (PSU), L.M. McCauley (PSU), J.A. Kennea (PSU) and V. D'Elia\nreport on behalf of the Swift-XRT team:\n\nWe have analysed 11 ks of XRT data for GRB 150817A (D'Elia et al. GCN\nCirc. 18143), from 56 s to 29.2 ks after the  BAT trigger. The data\ncomprise 32 s in Windowed Timing (WT) mode (the first 7 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 Osborne et\nal. (GCN Circ. 18146).\n\nThe light curve can be modelled with a series of power-law decays. The\ninitial decay index is alpha=3.6 (+/-0.4). At T+104 s  the decay\nflattens to an alpha of 0.57 (+0.06, -1.00) before breaking again at\nT+4285 s to a final decay with index alpha=1.07 (+/-0.07).\n\nA spectrum formed from the PC mode data can be fitted with an absorbed\npower-law with a photon spectral index of 1.77 (+/-0.11). The\nbest-fitting absorption column is  4.5 (+0.7, -0.6) x 10^21 cm^-2, in\nexcess of the Galactic value of 2.7 x 10^21 cm^-2 (Willingale et al.\n2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion\nfactor deduced from this spectrum  is 4.5 x 10^-11 (6.4 x 10^-11) erg\ncm^-2 count^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     4.5 (+0.7, -0.6) x 10^21 cm^-2\nGalactic foreground: 2.7 x 10^21 cm^-2\nExcess significance: 4.6 sigma\nPhoton index:\t     1.77 (+/-0.11)\n\nIf the light curve continues to decay with a power-law decay index of\n1.07, the count rate at T+24 hours will be 0.021 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 9.7 x\n10^-13 (1.4 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/00652334.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 18147,
  "createdOn": 1439820842000,
  "email": "pae9@leicester.ac.uk",
  "subject": "GRB 150817A: Swift-XRT refined Analysis",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>",
  "eventId": "GRB 150817A"
}