{
  "bibcode": "2004GCN..2808....1B",
  "body": "GRB041006: Fading X-ray Afterglow Observed with Chandra\n\nN. Butler, R. Vanderspek, H. L. Marshall, P. G. Ford, G. R. Ricker \n(MIT), D. Q. Lamb (U.Chicago), and G. P. Garmire (PSU)\n\nreport:\n\nBeginning at October 7.213 (t[burst] + 16.80 hr) and continuing until \nOctober 8.286 (t[burst] + 42.57 hr), Chandra Low Energy Transmission \nGrating Spectrometer (LETGS) observations were conducted of a field \ncentered on the optical afterglow candidate (Da Costa et al, GCN2765) for \nGRB041006, which was localized by the HETE WXM instrument (Galassi et al, \nGCN2770).  We have detected a moderately bright, fading X-ray afterglow \nconsistent in position with the optical source.  Over the 86.3 ksec of data \naccumulation (livetime) for the Chandra observations, the mean counting rate \nwas 0.010 counts/s in the dispersed 1st order LETGS spectrum and 0.007 \ncounts/s in the 0ther order.  The source we detected faded in brightness \naccording to a power law, with a decay time slope of -1.0 +/- 0.1.  We fit \nthe 0th order and 1st order data jointly, requiring 20 or more counts per \nspectral bin.  An absorbed power-law model provides an acceptable fit \n(chi^2/nu = 66.2/63), with the following best-fit paramters over the\n0.5-6 keV range:\n\ndN/dE = A * exp[-nH*s(E)] * E^ (-gamma) ph cm^(-2) s^(-1) keV^(-1) ,\nwith:\n\nA = (1.0+/-0.2) x 10^(-4) , \ngamma = 1.9+/-0.2 , and\nnH = (1.1+/-0.5) x 10^21 cm^(-2). \n\nThe measured value of nH exceeds the anticipated Galactic column density \n(nH = 2.9 x 10^20 cm^(-2)) in the source direction.  We measure a\nmean flux in the 0.5 to 6 keV band over the duration of the Chandra \nobservation of ~3.7 x 10^(-13) ergs cm^(-2) s^(-1).\n\nOur analyses are continuing, and more detailed results will be posted at:\n\nhttp://space.mit.edu/HETE/Bursts/GRB041006\n\nWe thank Harvey Tananbaum and the Chandra X-ray Observatory Operations \npersonnel, particularly Jeremy Drake and Brad Wargelin, for the impressive \npromptness with which this observation was planned and carried out.\n\nThe preliminary results reported here may be cited.",
  "circularId": 2808,
  "createdOn": 1097864211000,
  "email": "nrbutler@space.mit.edu",
  "subject": "GRB041006: Fading X-ray Afterglow Observed with Chandra",
  "submitter": "Nat Butler at MIT/CSR  <nrbutler@space.mit.edu>",
  "eventId": "GRB 041006"
}