{
  "bibcode": "2022GCN.33076....1A",
  "body": "E. Ambrosi  (INAF-IASFPA) , M. Capalbi (INAF-IASFPA), M. Perri (SSDC &\nINAF-OAR), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), A.P.\nBeardmore (U. Leicester), P.A. Evans (U. Leicester), J.P. Osborne (U.\nLeicester) and S. Dichiara report on behalf of the Swift-XRT team:\n\nWe have analysed 6.6 ks of XRT data for GRB 221216A (Dichiara et al.\nGCN Circ. 33067), from 61 s to 38.7 ks after the  BAT trigger. The data\ncomprise 249 s in Windowed Timing (WT) mode (the first 10 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 Evans et\nal. (GCN Circ. 33071).\n\nThe late-time light curve (from T0+4.6 ks) can be modelled with an\ninitial power-law decay with an index of alpha=0.30 (+0.16, -0.17),\nfollowed by a break at T+12.4 ks to an alpha of 2.2 (+0.4, -0.3).\n\nA spectrum formed from the WT mode data can be fitted with an absorbed\npower-law with a photon spectral index\tof 1.58 (+/-0.03). The\nbest-fitting absorption column is  1.49 (+0.13, -0.12) x 10^21 cm^-2,\nin excess of the Galactic value of 2.8 x 10^20 cm^-2 (Willingale et al.\n2013). The PC mode spectrum has a photon index of 1.75 (+0.12, -0.11)\nand a best-fitting absorption column of 5.1 (+2.9, -2.3) x 10^20 cm^-2.\nThe counts to observed (unabsorbed) 0.3-10 keV flux conversion factor\ndeduced from this spectrum  is 3.7 x 10^-11 (4.0 x 10^-11) erg cm^-2\ncount^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     5.1 (+2.9, -2.3) x 10^20 cm^-2\nGalactic foreground: 2.8 x 10^20 cm^-2\nExcess significance: <1.6 sigma\nPhoton index:\t     1.75 (+0.12, -0.11)\n\nIf the light curve continues to decay with a power-law decay index of\n2.2, the count rate at T+24 hours will be 6.3 x 10^-3 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.3 x\n10^-13 (2.5 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/01144698.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 33076,
  "createdOn": 1671235974000,
  "email": "pae9@leicester.ac.uk",
  "subject": "GRB 221216A: Swift-XRT refined Analysis",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>",
  "eventId": "GRB 221216A"
}