{
  "bibcode": "2015GCN.18216....1M",
  "body": "A. Melandri (INAF-OAB), P. D'Avanzo (INAF-OAB), D.N. Burrows (PSU),\nT.G.R. Roegiers (PSU), L.M. McCauley (PSU), K.L. Page (U. Leicester),\nC. Pagani (U. Leicester), A.P. Beardmore (U. Leicester), V. D'Elia\n(ASDC) and A.Y. Lien report on behalf of the Swift-XRT team:\n\nWe have analysed 8.6 ks of XRT data for GRB 150831A (Lien et al. GCN\nCirc. 18209), from 72 s to 22.5 ks after the  BAT trigger. The data\ncomprise 8 s in Windowed Timing (WT) mode (taken while Swift was\nslewing), with the remainder in Photon Counting (PC) mode. The enhanced\nXRT position for this burst was given by Osborne et al. (GCN Circ.\n18212).\n\nThe light curve can be modelled with a power-law decay with a decay\nindex of alpha=2.52 (+0.21, -0.22).\n\nA spectrum formed from the WT mode data can be fitted with an absorbed\npower-law with a photon spectral index\tof 1.25 (+0.17, -0.12). The\nbest-fitting absorption column is  1.27 (+0.89, -0.13) x 10^21 cm^-2,\nconsistent with the Galactic value of 1.1 x 10^21 cm^-2 (Willingale et\nal. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux\nconversion factor deduced from this spectrum  is 5.0 x 10^-11 (5.4 x\n10^-11) erg cm^-2 count^-1. \n\nA summary of the WT-mode spectrum is thus:\nTotal column:\t     1.27 (+0.89, -0.13) x 10^21 cm^-2\nGalactic foreground: 1.1 x 10^21 cm^-2\nExcess significance: <1.6 sigma\nPhoton index:\t     1.25 (+0.17, -0.12)\n\nIf the light curve continues to decay with a power-law decay index of\n2.52, the count rate at T+24 hours will be 2.1 x 10^-7 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.1 x\n10^-17 (1.2 x 10^-17) erg cm^-2 s^-1.\n\nThe results of the XRT-team automatic analysis are available at\nhttp://www.swift.ac.uk/xrt_products/00653838.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 18216,
  "createdOn": 1441061463000,
  "email": "pae9@leicester.ac.uk",
  "subject": "GRB 150831A: Swift-XRT refined Analysis",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>",
  "eventId": "GRB 150831A"
}