{
  "bibcode": "2019GCN.26609....1G",
  "body": "J. D. Gropp (PSU), A. Tohuvavohu (U. Toronto), J.A. Kennea (PSU), A.P.\nBeardmore (U. Leicester), P.A. Evans (U. Leicester), J.P. Osborne (U.\nLeicester), E. Ambrosi\t(INAF-IASFPA) , M. Capalbi (INAF-IASFPA) and\nM.G. Bernardini report on behalf of the Swift-XRT team:\n\nWe have analysed 7.7 ks of XRT data for GRB 191228A (Bernardini et al.\nGCN Circ. 26601), from 127 s to 48.0 ks after the  BAT trigger. The\ndata comprise 216 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. 26606).\n\nThe late-time light curve (from T0+5.4 ks) can be modelled with a\npower-law decay with a decay index of alpha=1.58 (+0.13, -0.12).\n\nA spectrum formed from the WT mode data can be fitted with an absorbed\npower-law with a photon spectral index\tof 1.96 (+/-0.05). The\nbest-fitting absorption column is  3.09 (+0.24, -0.23) x 10^21 cm^-2,\nin excess of the Galactic value of 3.8 x 10^20 cm^-2 (Willingale et al.\n2013). The PC mode spectrum has a photon index of 2.14 (+0.16, -0.15)\nand a best-fitting absorption column of 4.0 (+/-0.7) x 10^21 cm^-2. The\ncounts to observed (unabsorbed) 0.3-10 keV flux conversion factor\ndeduced from this spectrum  is 3.6 x 10^-11 (6.1 x 10^-11) erg cm^-2\ncount^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     4.0 (+/-0.7) x 10^21 cm^-2\nGalactic foreground: 3.8 x 10^20 cm^-2\nExcess significance: 8.7 sigma\nPhoton index:\t     2.14 (+0.16, -0.15)\n\nIf the light curve continues to decay with a power-law decay index of\n1.58, the count rate at T+24 hours will be 8.1 x 10^-3 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.9 x\n10^-13 (5.0 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/00946476.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 26609,
  "createdOn": 1577560956000,
  "email": "pae9@leicester.ac.uk",
  "subject": "GRB 191228A: Swift-XRT refined Analysis",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>",
  "eventId": "GRB 191228A"
}