{
  "bibcode": "2006GCN..5428....1G",
  "body": "O. Godet, K. L. Page, M. R. Goad, E. Rol, P.T. O'Brien (U Leicester),\nP. Schady (UCL-MSSL), and K. Hurley (UCB) report on behalf of the\nSwift-XRT team:\n\nGRB 060805B was detected by IPN (GNC Circ 5407). XRT started to observe\n35.1 hours after the IPN trigger for a present 25ks of data. The full\nIPN error box was within the XRT field of view. Using the ftool\nxrtcentroid, the first 25ks of the XRT data revealed an X-ray source in\nthe IPN error box at (J2000):\n\nRA =  18 10 05.56\nDec = +58 09 16.3\n\nwith an uncertainty of 3.9 arcseconds (90% containment). This position\nconsistent with that given by Butler 2006 (GCN Circ. 5414) does not\ncorrespond to any catalogued X-ray sources. We note that the X-ray\nposition is consistent with the position of two optical sources S1 and\nS2 in the USNO-B1.0 (Monet et al. 2003) and APM-North (McMahon et al.\n2000) catalogues, repectively.  The source S1 (RA(J2000) = 18 10 05.56\nand Dec = +58 09 19.3) is 2.9 arcseconds away from the XRT position. The\nsource S2 (RA(J2000) = 18 10 05.60 and Dec = +58 09 19.1) is 2.8\narcseconds away from the XRT position. The positions of the optical\nsources are consistent with those reported by Butler 2006 (GCN Circ.\n5414).\n\nThe spectrum from the first 19ks of the PC data can be well fitted by an\nabsorbed power-law with Gamma = 1.78 +0.36/-0.33. No clear evidence of\nabsorption in excess over the Galactic absorption (nH(Gal) = 3.7e20\ncm^-2 from Dickey & Lockman 1990) is seen in the data. The unabsorbed\nflux in the 0.5-10 keV energy band is 3.9 +1.8/-1.1e-13 erg cm^-2 s^-1.\nThese results are consistent with those given by Butler (2006; GCN Circ\n5414).\n\nUsing the initial 19ks of data did not allow us to determine if the\nX-source was really fading. Indeed, fitting the light-curve with a\nconstant (C) gives a value of chi^2/dof=6.5/7 with C = 0.0087+/-0.0012,\nwhile using a power-law gives a value of chi^2/dof=4.0/6 with alpha =\n1.62 +1.70/-1.56 (http://www.swift.ac.uk/grb060805b.shtml). Using a\npower-law allows an improvement of delta chi^2 = 2.5 for 1 dof i.e. less\nthan 90% confidence. \n\nAdding 6 ks of data obtained at later time allows us to confirm that the\nX-ray source is actually fading with a decay slope of alpha = 1.20\n+0.72/-0.53 (http://www.swift.ac.uk/grb060805b.shtml) and is likely to\nbe the afterglow of GRB 060805B.\n\nWe would like to encourage ground observations in order to determine the\nredshift of this burst.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 5428,
  "createdOn": 1155131400000,
  "email": "og19@star.le.ac.uk",
  "subject": "GRB 060805B: XRT Team Analysis",
  "submitter": "Olivier Godet at U.of Leicester  <og19@star.le.ac.uk>",
  "eventId": "GRB 060805B"
}