{
  "bibcode": "2009GCN..9940....1G",
  "body": "D. Grupe (PSU), P.A. Evans and M.R. Goad (U. Leicester) report\non behalf of the Swift-XRT team:\n\nWe have analysed  the first two orbits of XRT data of GRB090926B\n(Grupe et al. GCN Circ.  9935). The data comprise 307 s in Windowed\n  Timing (WT) mode and 1985 s in Photon Counting (PC) mode.\n\n\nUsing 1692 s of XRT Photon Counting mode data and 1 UVOT\nimages, we find an astrometrically corrected X-ray position (using\nthe XRT-UVOT alignment and matching UVOT field sources to the USNO-B1\ncatalogue): RA, Dec =\n46.30840, -39.00600 which is equivalent to:\n\nRA (J2000):  03 05 14.01\nDec (J2000): -39 00 21.5\n\nwith an uncertainty of 1.7\" (radius, 90% confidence). This\nposition is 32.7\" from the BAT ground-calculated position given in\nBaumgartner et al (GCN circular 9939).\n\nThis position may be improved as more data are received.  The latest\nposition can be viewed at http://www.swift.ac.uk/xrt_positions.\nPosition enhancement is described by Goad et al. (2007, A&A, 476,\n1401) and Evans et al. (2009, MNRAS, 397, 1177).\n\nA spectrum formed from the WT mode data can be fitted with an\nabsorbed  power-law with a photon spectral index of 1.84+/-0.07\nwith an   absorption column of (1.70+/-0.22)e21 cm^-2 which is in\nexcess of the Galactic value of 1.91 x 10^20 cm^-2 (Kalberla et al.\n2005). The PC mode spectrum results is a slightly flatter X-ray\nspectrum with Gamma = 1.58+0.22-0.20. The absorption column density,\nhowever, is consistent with the WT result. Based on the excess\nabsorption, according to Grupe et al. (2007, AJ, 133, 2216), the\nredshift of this burst is most likely less than 4.0.\n\n\nThe light curve can be modelled with a broken power-law decay with an\nindex of alpha=2.00+/-0.05, followed by a break at T+712+190/-160 s\nto  an alpha of 1.23 (-0.17, +0.07). If the afterglow continues to\ndacay with a slope of 1.23, the predicted count rate 24 hours after\nthe trigger is 3.4e-3 counts s^-1 or 1.6e-13 ergs s^-1 cm^-2.\n\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 9940,
  "createdOn": 1254025000000,
  "email": "grupe@astro.psu.edu",
  "subject": "GRB 090926B: Swift XRT refined analysis",
  "submitter": "Dirk Grupe at PSU/Swift-XRT  <grupe@astro.psu.edu>",
  "eventId": "GRB 090926B"
}