{
  "bibcode": "2018GCN.22376....1O",
  "body": "J.P. Osborne (U. Leicester), A.P. Beardmore (U. Leicester), A. Melandri\n(INAF-OAB), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), D.N. Burrows\n(PSU), A. Tohuvavohu (PSU), S. J. LaPorte (PSU) and K.L. Page report on\nbehalf of the Swift-XRT team:\n\nWe have analysed 8.0 ks of XRT data for GRB 180204A (Page et al. GCN\nCirc. 22375), from 90 s to 21.2 ks after the  BAT trigger. The data\ncomprise 32 s in Windowed Timing (WT) mode with the remainder in Photon\nCounting (PC) mode. The best available XRT position  (using the\npromptly downlinked event data, the XRT-UVOT alignment and matching\nUVOT field sources to the USNO-B1 catalogue) is RA, Dec = 330.1333,\n30.8381 which is equivalent to:\n\nRA (J2000): 22 00 32.00\nDec(J2000): +30 50 17.1\n\nwith an uncertainty of 2.1 arcsec (radius, 90% confidence).\n\nThe light curve can be modelled with a power-law decay with a decay\nindex of alpha=1.15 (+/-0.03).\n\nA spectrum formed from the PC mode data can be fitted with an absorbed\npower-law with a photon spectral index of 2.02 (+0.23, -0.22). The\nbest-fitting absorption column is  6.9 (+1.7, -1.5) x 10^21 cm^-2, in\nexcess of the Galactic value of 1.0 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 4.3 x 10^-11 (7.6 x 10^-11) erg\ncm^-2 count^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     6.9 (+1.7, -1.5) x 10^21 cm^-2\nGalactic foreground: 1.0 x 10^21 cm^-2\nExcess significance: 6.5 sigma\nPhoton index:\t     2.02 (+0.23, -0.22)\n\nIf the light curve continues to decay with a power-law decay index of\n1.15, the count rate at T+24 hours will be 2.7 x 10^-3 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.2 x\n10^-13 (2.0 x 10^-13) erg cm^-2 s^-1.\n\nThe results of the XRT-team automatic analysis are available at\nhttp://www.swift.ac.uk/xrt_products/00808483.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 22376,
  "createdOn": 1517739983000,
  "email": "pae9@leicester.ac.uk",
  "subject": "GRB 180204A: Swift-XRT refined Analysis",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>",
  "eventId": "GRB 180204A"
}