{
  "bibcode": "2010GCN.10588....1C",
  "body": "S. Campana (INAF-OAB), P.A. Evans (U. Leicester) and S. T. Holland\n(CRESST/USRA/GSFC) report on behalf of the Swift-XRT team:\n\nSwift XRT observed GRB 100413A (Holland et al. 2010, GCN 10581)\nin Windowed Timing (WT) mode in the 146-550 s time interval.\nDuring this interval the 1.5-10 keV to 0.3-1.5 keV hardness ratio slightly\ndecayed, testifying for small spectral variations.\nWe assume a Galactic column density of 7.3x10^20 cm^-2 (Kalberla et\nal. 2005, A&A 440 775) and fit the WT spectrum with an absorbed\n(tbabs*ztbabs) cutoff power law model within XSPEC (the cutoff power\nlaw model provides much better results in terms of column density \nevaluation\nwith respect to a simple power law model when small spectral variations \nare present).\nData were grouped to have 30 counts per spectral bin. The resulting fit \nis good\n(reduced chi2=0.9, 194 dof).\nFiltering the data for single pixel events does not change the results.\nIn the intrinsic column density vs. redshift plane there is a low \nsignificance (3 sigma)\nsolution at low redshifts but the minimum lies at higher redshifts with \na 2 sigma confidence\nlevel solution of z=3.9+1.7-0.7 and N_H(z)=(5.5+9.8-2.1)x1022 cm-2.\nThus, even if we cannot exclude that GRB100413A is at low redshift, a \nhigh redshift (z~4),\nhighly absorbed (N_H(z)~6x1022 cm-2) solution is preferred.\nThis compares well with the non-detection with UVOT (Holland et al. \n2010) and\nother robotic telescopes.\n\nThe contour plot is available at\nhttp://www.brera.inaf.it/utenti/campana/100413.gif",
  "circularId": 10588,
  "createdOn": 1271241580000,
  "email": "sergio.campana@brera.inaf.it",
  "subject": "Tentative redshift of GRB100413A from X-ray data",
  "submitter": "Sergio Campana at INAF-OAB  <sergio.campana@brera.inaf.it>",
  "eventId": "GRB 100413A"
}