{
  "bibcode": "2019GCN.26559....1D",
  "body": "P. D'Avanzo (INAF-OAB), D.N. Burrows (PSU), J. D. Gropp (PSU), A.\nTohuvavohu (U. Toronto), K.L. Page (U. Leicester), A.P. Beardmore (U.\nLeicester), P.A. Evans (U. Leicester), M.G. Bernardini (INAF-OAB), E.\nAmbrosi  (INAF-IASFPA)\tand S Laha report on behalf of the Swift-XRT\nteam:\n\nWe have analysed 7.8 ks of XRT data for GRB 191221B (S Laha et al. GCN\nCirc. 26534), from 74 s to 58.6 ks after the  BAT trigger. The data\ncomprise 1.3 ks in Windowed Timing (WT) mode (the first 8 s were taken\nwhile Swift was slewing) with the remainder in Photon Counting (PC)\nmode. The enhanced XRT position for this burst was given by Beardmore\net al. (GCN Circ. 26540).\n\nThe late-time light curve (from T0+4.9 ks) can be modelled with a\npower-law decay with a decay index of alpha=1.03 (+0.09, -0.08).\n\nA spectrum formed from the WT mode data can be fitted with an absorbed\npower-law with a photon spectral index\tof 2.097 (+/-0.014). The\nbest-fitting absorption column is  consistent with the Galactic value\nof 8.6 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has\na photon index of 1.86 (+0.07, -0.06) and a best-fitting absorption\ncolumn consistent with the Galactic value. The counts to observed\n(unabsorbed) 0.3-10 keV flux conversion factor deduced from this\nspectrum  is 3.6 x 10^-11 (4.1 x 10^-11) erg cm^-2 count^-1. \n\nA summary of the PC-mode spectrum is thus:\nGalactic foreground: 8.6 x 10^20 cm^-2\nIntrinsic column:    8.6 (+5.8, -0.0) x 10^20 cm^-2 at z=1.148\nPhoton index:\t     1.86 (+0.07, -0.06)\n\nIf the light curve continues to decay with a power-law decay index of\n1.03, the count rate at T+24 hours will be 0.087 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.1 x\n10^-12 (3.6 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/00945521.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 26559,
  "createdOn": 1577037428000,
  "email": "pae9@leicester.ac.uk",
  "subject": "GRB 191221B: Swift-XRT refined Analysis",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>",
  "eventId": "GRB 191221B"
}