{
  "bibcode": "2015GCN.18127....1B",
  "body": "D.N. Burrows (PSU), C. Pagani (U. Leicester), A.P. Beardmore (U.\nLeicester), A. Melandri (INAF-OAB), P. D'Avanzo (INAF-OAB), V. D'Elia\n(ASDC), T.G.R. Roegiers (PSU), L.M. McCauley (PSU) and P.A. Evans\nreport on behalf of the Swift-XRT team:\n\nWe have analysed 8.5 ks of XRT data for GRB 150811A (Evans et al. GCN\nCirc. 18119), from 128 s to 27.8 ks after the  BAT trigger. The data\ncomprise 156 s in Windowed Timing (WT) mode (the first 9 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. 18124).\n\nThe light curve can be modelled with an initial power-law decay with an\nindex of alpha=2.52 (+/-0.19), followed by a break at T+366 s to an\nalpha of 1.17 (+0.06, -0.10).\n\nA spectrum formed from the WT mode data can be fitted with an absorbed\npower-law with a photon spectral index\tof 2.11 (+0.21, -0.13). The\nbest-fitting absorption column is  1.60 (+0.65, -0.07) x 10^21 cm^-2,\nconsistent with the Galactic value of 1.5 x 10^21 cm^-2 (Willingale et\nal. 2013). The PC mode spectrum has a photon index of 2.03 (+0.13,\n-0.15) and a best-fitting absorption column of 2.1 (+1.0, -0.6) x 10^21\ncm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion\nfactor deduced from this spectrum  is 3.5 x 10^-11 (4.9 x 10^-11) erg\ncm^-2 count^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     2.1 (+1.0, -0.6) x 10^21 cm^-2\nGalactic foreground: 1.5 x 10^21 cm^-2\nExcess significance: <1.6 sigma\nPhoton index:\t     2.03 (+0.13, -0.15)\n\nIf the light curve continues to decay with a power-law decay index of\n1.17, the count rate at T+24 hours will be 3.2 x 10^-3 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.1 x\n10^-13 (1.6 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/00651882.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 18127,
  "createdOn": 1439310062000,
  "email": "pae9@leicester.ac.uk",
  "subject": "GRB 150811A: Swift-XRT refined Analysis",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>",
  "eventId": "GRB 150811A"
}