{
  "bibcode": "2015GCN.18749....1O",
  "body": "J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A. D'Ai\n(INAF-IASFPA), A. Maselli  (INAF-IASFPA), A. Melandri (INAF-OAB), J.A.\nKennea (PSU), B. Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU), C.\nPagani (U. Leicester) and A.Y. Lien report on behalf of the Swift-XRT\nteam:\n\nWe have analysed 10 ks of XRT data for GRB 151228B (Lien et al. GCN\nCirc. 18739), from 40 s to 29.0 ks after the  BAT trigger. The data\ncomprise 194 s 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 Goad et al.\n(GCN Circ. 18743).\n\nThe late-time light curve (from T0+4.7 ks) can be modelled with a\npower-law decay with a decay index of alpha=0.68 (+0.22, -0.21).\n\nA spectrum formed from the WT mode data can be fitted with an absorbed\npower-law with a photon spectral index\tof 2.43 (+/-0.08). The\nbest-fitting absorption column is  1.78 (+0.21, -0.20) x 10^21 cm^-2,\nin excess of the Galactic value of 5.7 x 10^20 cm^-2 (Willingale et al.\n2013). The PC mode spectrum has a photon index of 1.94 (+0.14, -0.12)\nand a best-fitting absorption column consistent with the Galactic\nvalue. The counts to observed (unabsorbed) 0.3-10 keV flux conversion\nfactor deduced from this spectrum  is 3.4 x 10^-11 (3.7 x 10^-11) erg\ncm^-2 count^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     5.7 (+2.3, -0.0) x 10^20 cm^-2\nGalactic foreground: 5.7 x 10^20 cm^-2\nExcess significance: <1.6 sigma\nPhoton index:\t     1.94 (+0.14, -0.12)\n\nIf the light curve continues to decay with a power-law decay index of\n0.68, the count rate at T+24 hours will be 8.8 x 10^-3 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.0 x\n10^-13 (3.2 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/00668641.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 18749,
  "createdOn": 1451383913000,
  "email": "pae9@leicester.ac.uk",
  "subject": "GRB 151228B: Swift-XRT refined Analysis",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>",
  "eventId": "GRB 151228B"
}