{
  "bibcode": "2013GCN.15474....1S",
  "body": "M. C. Stroh and J. A. Kennea (PSU) report on behalf of the Swift-XRT\nteam:\n\nWe have analysed 7.9 ks of XRT data for the Fermi/LAT-detected burst:\nGRB 131108A,  from 25.9 ks to 49.8 ks after the  Fermi/LAT trigger. The\ndata are entirely in Photon Counting (PC) mode.  An X-ray source is\ndetected within the Fermi/LAT error circle. Using 4560 s of PC mode\ndata and 6 UVOT images, we find an enhanced XRT position (using the\nXRT-UVOT alignment and matching UVOT field sources to the USNO-B1\ncatalogue): RA, Dec = 156.50178, +9.66248 which is equivalent to:\n\nRA (J2000): 10h 26m 00.43s\nDec(J2000): +09d 39' 44.9\"\n\nwith an uncertainty of 1.6 arcsec (radius, 90% confidence). This\nposition is 14.4 arcmin from the center of the Fermi/LAT error circle\n(GCN #15464), consistant with that position, and inside the   \nIPN error box (GCN #15466).\n\nThe light curve can be modelled with  a power-law decay with a decay\nindex of alpha=1.9 (+0.7, -0.6).\n\nA spectrum formed from the PC mode data can be fitted with an absorbed\npower-law with a photon spectral index of 2.2 (+0.4, -0.3). The\nbest-fitting absorption column is  9.9 (+7.6, -6.5) x 10^20 cm^-2, in\nexcess of the Galactic value of 3.2 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 3.2 x 10^-11 (4.5 x 10^-11) erg\ncm^-2 count^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     9.9 (+7.6, -6.5) x 10^20 cm^-2\nGalactic foreground: 3.2 x 10^20 cm^-2\nExcess significance: 1.7 sigma\nPhoton index:\t     2.2 (+0.4, -0.3)\n\nIf the light curve continues to decay with a power-law decay index of\n1.9, the count rate at T+24 hours will be 5.2 x 10^-3 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.7 x\n10^-13 (2.4 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/00020326.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 15474,
  "createdOn": 1384010793000,
  "email": "stroh@astroh.org",
  "subject": "GRB 131108A: Swift-XRT observations",
  "submitter": "Michael Stroh at PSU/Swift  <stroh@astroh.org>",
  "eventId": "GRB 131108A"
}