{
  "bibcode": "2016GCN.19763....1D",
  "body": "P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), T.G.R. Roegiers (PSU), L.M.\nMcCauley (PSU), J.A. Kennea (PSU), A.P. Beardmore (U. Leicester), P.A.\nEvans (U. Leicester), S.L. Gibson (U. Leicester), A. D'Ai (INAF-IASFPA)\nand F.E. Marshall report on behalf of the Swift-XRT team:\n\nWe have analysed 6.1 ks of XRT data for GRB 160804A (Marshall et al.\nGCN Circ. 19761), from 137 s to 18.0 ks after the  BAT trigger. The\ndata comprise 600 s in Windowed Timing (WT) mode (the first 9 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\nOsborne et al. (GCN Circ. 19762).\n\nThe late-time light curve (from T0+4.3 ks) can be modelled with a\npower-law decay with a decay index of alpha=0.32 (+0.20, -0.19).\n\nA spectrum formed from the WT mode data can be fitted with an absorbed\npower-law with a photon spectral index\tof 1.772 (+/-0.023). The\nbest-fitting absorption column is  1.44 (+/-0.08) x 10^21 cm^-2, in\nexcess of the Galactic value of 1.9 x 10^20 cm^-2 (Willingale et al.\n2013). The PC mode spectrum has a photon index of 1.90 (+0.17, -0.16)\nand a best-fitting absorption column of 7.1 (+4.3, -3.8) x 10^20 cm^-2.\nThe counts to observed (unabsorbed) 0.3-10 keV flux conversion factor\ndeduced from this spectrum  is 3.4 x 10^-11 (4.0 x 10^-11) erg cm^-2\ncount^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     7.1 (+4.3, -3.8) x 10^20 cm^-2\nGalactic foreground: 1.9 x 10^20 cm^-2\nExcess significance: 2.2 sigma\nPhoton index:\t     1.90 (+0.17, -0.16)\n\nIf the light curve continues to decay with a power-law decay index of\n0.32, the count rate at T+24 hours will be 0.049 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.7 x\n10^-12 (1.9 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/00707231.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 19763,
  "createdOn": 1470303549000,
  "email": "pae9@leicester.ac.uk",
  "subject": "GRB 160804A: Swift-XRT refined Analysis",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>",
  "eventId": "GRB 160804A"
}