{
  "bibcode": "2013GCN.15154....1S",
  "body": "M.C. Stroh (PSU), D.N. Burrows (PSU), J.A. Kennea (PSU), A.P. Beardmore\n(U. Leicester), P.A. Evans (U. Leicester), B.P. Gompertz (U.\nLeicester), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), A. Maselli \n(INAF-IASFPA) and D. Malesani report on behalf of the Swift-XRT team:\n\nWe have analysed 6.8 ks of XRT data for GRB 130831B (Malesani  et al.\nGCN Circ. 15141),  from 112 s to 35.4 ks after the  BAT trigger. The\ndata comprise 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 Goad et al. (GCN. Circ 15149).\n\nThe late-time light curve (from T0+5.1 ks) can be modelled with  a\npower-law decay with a decay index of alpha=1.24 (+0.12, -0.11).\n\nA spectrum formed from the PC mode data can be fitted with an absorbed\npower-law with a photon spectral index of 2.07 (+0.16, -0.15). The\nbest-fitting absorption column is  1.6 (+/-0.4) x 10^21 cm^-2, in\nexcess of the Galactic value of 6.2 x 10^20 cm^-2 (Kalberla et al.\n2005). The counts to observed (unabsorbed) 0.3-10 keV flux conversion\nfactor deduced from this spectrum  is 3.7 x 10^-11 (5.3 x 10^-11) erg\ncm^-2 count^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     1.6 (+/-0.4) x 10^21 cm^-2\nGalactic foreground: 6.2 x 10^20 cm^-2\nExcess significance: 4.2 sigma\nPhoton index:\t     2.07 (+0.16, -0.15)\n\nIf the light curve continues to decay with a power-law decay index of\n1.24, the count rate at T+24 hours will be 9.4 x 10^-3 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.5 x\n10^-13 (5.0 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/00568855.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 15154,
  "createdOn": 1378008783000,
  "email": "pae9@leicester.ac.uk",
  "subject": "GRB 130831B: Swift-XRT refined Analysis",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>",
  "eventId": "GRB 130831B"
}