{
  "bibcode": "2014GCN.15648....1M",
  "body": "V. Mangano (PSU), K. Page (U. Leicester), D. Malesani (DARK/NBI) \nreport on behalf of the Swift-XRT team:\n\nWe have analysed 4.0 ks of XRT data for the Fermi/LAT-detected burst:\nGRB 131231A,  from 52.1 ks to 62.5 ks after the  Fermi/LAT trigger. The\ndata are entirely in Photon Counting (PC) mode. \nAn X-ray source is detected at a position consistent with the optical afterglow \n(Xu et al., GCN 15641) at a mean count rate of 0.4 ct/s.\nThe refined XRT position is RA, Dec = 10.5904, -1.6519  which is equivalent to:\n\nRA (J2000): 00 42 21.70\nDec(J2000): -01 39 06.7\n\nwith an uncertainty of 3.5 arcsec (radius, 90% confidence). This\nposition is 695 arcsec from the Fermi/LAT position and 4 arcsec\nfrom the optical afterglow.\n\nThe light curve can be modelled with a power-law decay with an\nindex of alpha=1.6 (+/-0.7). \n\nA spectrum formed from the PC mode data can be fitted with an absorbed\npower-law with a photon spectral index of 1.86 (+0.13, -0.13). The\nbest-fitting absorption column at the redshift of 0.642 (Xu et al., GCN 15645)\nis  1.4 (+0.7, -0.6) x 10^21 cm^-2, in excess of the Galactic value of \n2.6 x 10^20 cm^-2 (Kalberla et al. 2005). \nThe counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced \nfrom this spectrum  is 3.0 x 10^-11 (4.0 x 10^-11) erg cm^-2 count^-1. \n\nFurther ToO observations have already been scheduled for today.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 15648,
  "createdOn": 1388597966000,
  "email": "vxm22@psu.edu",
  "subject": "GRB 131231A: Swift-XRT observations",
  "submitter": "Vanessa Mangano at PSU  <vxm22@psu.edu>",
  "eventId": "GRB 131231A"
}