{
  "bibcode": "2020GCN.29108....1B",
  "body": "A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), E. Ambrosi \n(INAF-IASFPA) , M. Capalbi (INAF-IASFPA), M. Perri (SSDC & INAF-OAR),\nD.N. Burrows (PSU), J. D. Gropp (PSU), J.A. Kennea (PSU), J.P. Osborne\n(U. Leicester) and K.L. Page report on behalf of the Swift-XRT team:\n\nWe have analysed 6.2 ks of XRT data for GRB 201221A (Page et al. GCN\nCirc. 29096), from 143 s to 23.8 ks after the  BAT trigger. The data\ncomprise 320 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. 29097).\n\nThe light curve can be modelled with a power-law decay with a decay\nindex of alpha=0.71 (+/-0.04).\n\nA spectrum formed from the PC mode data can be fitted with an absorbed\npower-law with a photon spectral index of 1.39 (+0.16, -0.15). The\nbest-fitting absorption column is  6.3 (+8.3, -6.3) x 10^22 cm^-2, at a\nredshift of 5.7, in addition to the Galactic value of 9.3 x 10^20 cm^-2\n(Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10\nkeV flux conversion factor deduced from this spectrum  is 5.0 x 10^-11\n(4.7 x 10^-11) erg cm^-2 count^-1. \n\nA summary of the PC-mode spectrum is thus:\nGalactic foreground: 9.3 x 10^20 cm^-2\nIntrinsic column:    6.3 (+8.3, -6.3) x 10^22 cm^-2 at z=5.7\nPhoton index:\t     1.39 (+0.16, -0.15)\n\nIf the light curve continues to decay with a power-law decay index of\n0.71, the count rate at T+24 hours will be 0.016 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 8.0 x\n10^-13 (7.4 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/01013852.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 29108,
  "createdOn": 1608587851000,
  "email": "pae9@leicester.ac.uk",
  "subject": "GRB 201221A: Swift-XRT refined Analysis",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>",
  "eventId": "GRB 201221A"
}