{
  "bibcode": "2018GCN.23584....1L",
  "body": "S. J. LaPorte (PSU), J.A. Kennea (PSU), B. Sbarufatti (INAF-OAB/PSU),\nA.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), J.P. Osborne\n(U. Leicester), A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAB), P.\nD'Avanzo (INAF-OAB) and M.J. Moss report on behalf of the Swift-XRT\nteam:\n\nWe have analysed 6.2 ks of XRT data for GRB 181228A (Moss et al. GCN\nCirc. 23570), from 88 s to 58.6 ks after the  BAT trigger. The data\ncomprise 405 s in Windowed Timing (WT) mode with the remainder in\nPhoton Counting (PC) mode. The enhanced XRT position for this burst was\ngiven by Beardmore et al. (GCN Circ. 23574).\n\nThe late-time light curve (from T0+12.9 ks) can be modelled with a\npower-law decay with a decay index of alpha=0.95 (+0.29, -0.28).\n\nA spectrum formed from the WT mode data can be fitted with an absorbed\npower-law with a photon spectral index\tof 1.60 (+/-0.05). The\nbest-fitting absorption column is  3.30 (+0.28, -0.27) x 10^21 cm^-2,\nin excess of the Galactic value of 2.9 x 10^21 cm^-2 (Willingale et al.\n2013). The PC mode spectrum has a photon index of 1.80 (+0.20, -0.19)\nand a best-fitting absorption column of 5.3 (+1.4, -1.2) x 10^21 cm^-2.\nThe counts to observed (unabsorbed) 0.3-10 keV flux conversion factor\ndeduced from this spectrum  is 4.6 x 10^-11 (6.8 x 10^-11) erg cm^-2\ncount^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     5.3 (+1.4, -1.2) x 10^21 cm^-2\nGalactic foreground: 2.9 x 10^21 cm^-2\nExcess significance: 3.2 sigma\nPhoton index:\t     1.80 (+0.20, -0.19)\n\nIf the light curve continues to decay with a power-law decay index of\n0.95, the count rate at T+24 hours will be 0.012 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.7 x\n10^-13 (8.4 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/00879909.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 23584,
  "createdOn": 1546030297000,
  "email": "pae9@leicester.ac.uk",
  "subject": "GRB 181228A: Swift-XRT refined Analysis",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>",
  "eventId": "GRB 181228A"
}