{
  "bibcode": "2018GCN.23083....1L",
  "body": "S. J. LaPorte (PSU), J.A. Kennea (PSU), K.L. Page (U. Leicester), A.P.\nBeardmore (U. Leicester), P.A. Evans (U. Leicester), A. Melandri\n(INAF-OAB), V. D'Elia (ASDC), B. Sbarufatti (INAF-OAB/PSU) and P.\nD'Avanzo report on behalf of the Swift-XRT team:\n\nWe have analysed 6.6 ks of XRT data for GRB 180805B (D'Avanzo et al.\nGCN Circ. 23076), from 82 s to 36.7 ks after the  BAT trigger. The data\ncomprise 197 s in Windowed Timing (WT) mode with the remainder in\nPhoton Counting (PC) mode. The enhanced XRT position for this burst was\ngiven by Evans et al. (GCN Circ. 23077).\n\nThe light curve can be modelled with a series of power-law decays. The\nlight curve initially rises, with an index alpha=-1.5 (+0.0, -0.5). At\nT+102 s it breaks to an alpha of 1.61 (+0.15, -0.65). The light curve\nbreaks again at T+241 s to a decay with alpha=3.1 (+/-0.4),  before a\nfinal break at T+891 s s after which the decay index is 0.88 (+0.21,\n-0.18).\n\nA spectrum formed from the WT mode data can be fitted with an absorbed\npower-law with a photon spectral index\tof 0.93 (+0.09, -0.06). The\nbest-fitting absorption column is  2.3 (+4.7, -0.7) x 10^20 cm^-2,\nconsistent with the Galactic value of 1.6 x 10^20 cm^-2 (Willingale et\nal. 2013). The PC mode spectrum has a photon index of 1.90 (+0.25,\n-0.23) and a best-fitting absorption column of 7.3 (+6.6, -5.4) x 10^20\ncm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion\nfactor deduced from this spectrum  is 3.5 x 10^-11 (4.0 x 10^-11) erg\ncm^-2 count^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     7.3 (+6.6, -5.4) x 10^20 cm^-2\nGalactic foreground: 1.6 x 10^20 cm^-2\nExcess significance: 1.7 sigma\nPhoton index:\t     1.90 (+0.25, -0.23)\n\nIf the light curve continues to decay with a power-law decay index of\n0.88, the count rate at T+24 hours will be 2.0 x 10^-3 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 6.8 x\n10^-14 (7.8 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/00851855.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 23083,
  "createdOn": 1533520986000,
  "email": "pae9@leicester.ac.uk",
  "subject": "GRB 180805B: Swift-XRT refined Analysis",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>",
  "eventId": "GRB 180805B"
}