{
  "bibcode": "2015GCN.18194....1M",
  "body": "A. Maselli  (INAF-IASFPA), A. Melandri (INAF-OAB), P. D'Avanzo\n(INAF-OAB), B. Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU), T.G.R.\nRoegiers (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester),\nC. Pagani (U. Leicester) and E. Troja report on behalf of the Swift-XRT\nteam:\n\nWe have analysed 7.7 ks of XRT data for GRB 150821A (Troja et al. GCN\nCirc. 18186), from 233 s to 40.6 ks after the  BAT trigger. The data\ncomprise 1.1 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 Goad et al.\n(GCN Circ. 18191).\n\nThe late-time light curve (from T0+5.9 ks) can be modelled with a\npower-law decay with a decay index of alpha=1.26 (+0.15, -0.13).\n\nA spectrum formed from the WT mode data can be fitted with an absorbed\npower-law with a photon spectral index\tof 1.85 (+/-0.03). The\nbest-fitting absorption column is  1.66 (+0.09, -0.08) x 10^22 cm^-2,\nat a redshift of 0.755, in addition to the Galactic value of 1.8 x\n10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon\nindex of 2.21 (+/-0.15) and a best-fitting absorption column of 2.2\n(+0.4, -0.3) x 10^22 cm^-2. The counts to observed (unabsorbed) 0.3-10\nkeV flux conversion factor deduced from this spectrum  is 3.7 x 10^-11\n(7.1 x 10^-11) erg cm^-2 count^-1. \n\nA summary of the PC-mode spectrum is thus:\nGalactic foreground: 1.8 x 10^20 cm^-2\nIntrinsic column:    2.2 (+0.4, -0.3) x 10^22 cm^-2 at z=0.755\nPhoton index:\t     2.21 (+/-0.15)\n\nIf the light curve continues to decay with a power-law decay index of\n1.26, the count rate at T+24 hours will be 8.4 x 10^-3 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.1 x\n10^-13 (6.0 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/00652847.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 18194,
  "createdOn": 1440201543000,
  "email": "pae9@leicester.ac.uk",
  "subject": "GRB 150821A: Swift-XRT refined Analysis",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>",
  "eventId": "GRB 150821A"
}