{
  "bibcode": "2015GCN.18082....1P",
  "body": "K.L. Page (U. Leicester), C. Pagani (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), A.P.\nBeardmore (U. Leicester) and S.B. Cenko report on behalf of the\nSwift-XRT team:\n\nWe have analysed 8.0 ks of XRT data for GRB 150727A (Cenko et al. GCN\nCirc. 18076), from 68 s to 32.5 ks after the  BAT trigger. The data\ncomprise 523 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 Osborne et\nal. (GCN Circ. 18079).\n\nThe light curve can be modelled with a series of power-law decays. The\ninitial decay index is alpha=1.2 (+/-0.4). At T+93.8 s\tthe decay\nsteepens to an alpha of 2.72 (+0.11, -0.08). The light curve breaks\nagain at T+195 s to a decay with alpha=1.42 (+0.07, -0.06),  and  again\nat T+3169 s s to alpha=8.0 (+0.0, -5.8),  before a final break at\nT+4539 s s after which the decay index is 0.5 (+/-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 2.39 (+/-0.04). The\nbest-fitting absorption column is  2.0 (+/-1.5) x 10^20 cm^-2, at a\nredshift of 0.313, in addition to the Galactic value of 9.8 x 10^20\ncm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed)\n0.3-10 keV flux conversion factor deduced from this spectrum  is 2.7 x\n10^-11 (3.9 x 10^-11) erg cm^-2 count^-1. \n\nA summary of the WT-mode spectrum is thus:\nGalactic foreground: 9.8 x 10^20 cm^-2\nIntrinsic column:    2.0 (+/-1.5) x 10^20 cm^-2 at z=0.313\nPhoton index:\t     2.39 (+/-0.04)\n\nIf the light curve continues to decay with a power-law decay index of\n0.5, the count rate at T+24 hours will be 8.7 x 10^-3 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.4 x\n10^-13 (3.4 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/00650530.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 18082,
  "createdOn": 1438071842000,
  "email": "pae9@leicester.ac.uk",
  "subject": "GRB 150727A: Swift-XRT refined Analysis",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>",
  "eventId": "GRB 150727A"
}