{
  "bibcode": "2017GCN.21414....1B",
  "body": "D.N. Burrows (PSU), K.L. Page (U. Leicester), B. Mingo (U. Leicester),\nA.P. Beardmore (U. Leicester), P. D'Avanzo (INAF-OAB), V. D'Elia\n(ASDC), A. D'Ai (INAF-IASFPA), S. J. LaPorte (PSU) and A. Cholden-Brown\nreport on behalf of the Swift-XRT team:\n\nWe have analysed 6.5 ks of XRT data for GRB 170804A (Cholden-Brown et\nal. GCN Circ. 21410), from 112 s to 19.6 ks after the  BAT trigger. The\ndata comprise 95 s in Windowed Timing (WT) mode (the first 8 s were\ntaken while Swift was slewing) with the remainder in Photon Counting\n(PC) mode. The enhanced XRT position for this burst was given by Evans\net al. (GCN Circ. 21413).\n\nThe light curve can be modelled with an initial power-law decay with an\nindex of alpha=2.90 (+0.34, -0.22), followed by a break at T+519 s to\nan alpha of 1.13 (+0.20, -0.13).\n\nA spectrum formed from the WT mode data can be fitted with an absorbed\npower-law with a photon spectral index\tof 2.37 (+0.16, -0.13). The\nbest-fitting absorption column is  consistent with the Galactic value\nof 1.8 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has\na photon index of 1.97 (+0.16, -0.14) and a best-fitting absorption\ncolumn consistent with the Galactic value. The counts to observed\n(unabsorbed) 0.3-10 keV flux conversion factor deduced from this\nspectrum  is 3.2 x 10^-11 (3.4 x 10^-11) erg cm^-2 count^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     1.8 (+2.4, -0.0) x 10^20 cm^-2\nGalactic foreground: 1.8 x 10^20 cm^-2\nExcess significance: <1.6 sigma\nPhoton index:\t     1.97 (+0.16, -0.14)\n\nIf the light curve continues to decay with a power-law decay index of\n1.13, the count rate at T+24 hours will be 8.3 x 10^-4 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.7 x\n10^-14 (2.8 x 10^-14) erg cm^-2 s^-1.\n\nThe results of the XRT-team automatic analysis are available at\nhttp://www.swift.ac.uk/xrt_products/00766194.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 21414,
  "createdOn": 1501876888000,
  "email": "pae9@leicester.ac.uk",
  "subject": "GRB 170804A: Swift-XRT refined Analysis",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>",
  "eventId": "GRB 170804A"
}