{
  "bibcode": "2013GCN.14588....1D",
  "body": "P. D'Avanzo, A. Melandri (INAF-OAB), P.A. Evans (U. Leicester) report on\nbehalf of the Swift-XRT team:\n\nWe have analysed 7.7 ks of XRT data for the Fermi-LAT-detected burst: GRB\n130504C,  from 65.6 ks to 93.3 ks after the  Fermi-LAT trigger. The data\nare entirely in Photon Counting (PC) mode. The  X-ray source reported by\nD'Avanzo et al. (GCN Circ. 14584) displays behaviour consistent with\nfading. We propose it as the X-ray afterglow of GRB 130504C.\n\nThe refined XRT position is RA, Dec = 91.63038, +3.8339 which is\nequivalent to:\n\nRA (J2000): 06 06 31.29\nDec(J2000): +03 50 02.0\n\nwith an uncertainty of 3.6 arcsec (radius, 90% confidence).\n\nThe light curve can be modelled with  a power-law decay with a decay index\nof alpha=1.3 (+/-1.0).\n\nA spectrum formed from the PC mode data can be fitted with an absorbed\npower-law with a photon spectral index of 1.8 (+/-0.3). The best-fitting\nabsorption column is  5.1 (+2.0, -1.6) x 10^21 cm^-2, in excess of the\nGalactic value of 2.5 x 10^21 cm^-2 (Kalberla et al. 2005). The counts to\nobserved (unabsorbed) 0.3-10 keV flux conversion factor deduced from this\nspectrum  is 5.0 x 10^-11 (7.9 x 10^-11) erg cm^-2 count^-1.\n\nA summary of the PC-mode spectrum is thus:\nTotal column:             5.1 (+2.0, -1.6) x 10^21 cm^-2\nGalactic foreground: 2.5 x 10^21 cm^-2\nExcess significance: 2.7 sigma\nPhoton index:             1.8 (+/-0.3)\n\nThe results of the XRT-team automatic analysis are available at\nhttp://www.swift.ac.uk/xrt_products/00020267.\n\nThis circular is an official product of the Swift-XRT team.\n\n[GCN OPS NOTE(06may13): Per author's request, the extra \"further\" was removed\nfrom the ubject-line.]",
  "circularId": 14588,
  "createdOn": 1367849668000,
  "email": "paolo.davanzo@brera.inaf.it",
  "subject": "GRB 130504C: further Swift-XRT observations",
  "submitter": "Paolo D'Avanzo at INAF-OAB  <paolo.davanzo@brera.inaf.it>",
  "eventId": "GRB 130504C"
}