{
  "bibcode": "2002GCN..1504....1V",
  "body": "GRB020813: Fading X-ray Afterglow Observed with Chandra\n\nR. Vanderspek, H. L. Marshall, P. G. Ford, and G. R. Ricker (MIT \nCenter for Space Research)\n\nreport:\n\nBeginning at August 13.990 (t[burst] + 21.02 hr) and continuing until \nAugust 14.892 (t[burst] + 42.67 hr), Chandra High Energy Transmission \nGrating Spectrometer (HETGS) observations were conducted of a field \ncentered on the optical afterglow candidate (Fox et al, GCN1470) for \nGRB020813, which was accurately localized by both the HETE WXM and \nSXC instruments (Villasenor et al, GCN1471; Jernigan et al, GCN1494). \nWe have detected a moderately bright, fading X-ray afterglow \nconsistent in position with the optical source (Henden et al, \nGCN1478). Over the 76.8 ksec of data accumulation (livetime) for the \nChandra observations, the mean counting rate was 0.19 counts/s \n(summed over the dispersed signal from the HEG and the MEG gratings, \nand including the 0th order flux). The source we detected faded in \nbrightness according to a power law, with a decay time slope of -1.42 \n+/- 0.05. (This value is remarkably close to the decay slope values \nnear -1.4 being reported for the afterglow of GRB020813 in the \noptical; e.g. Malesani et al, GCN1500, and references therein.) The \nsource spectrum we derive from our preliminary analysis of the \ndispersed HETGS counts is characterized as follows:\n\nnH = 7 x 10^20 cm^(-2), consistent with the anticipated galactic \nabsorption in the source direction;\n\ndN/dE = A * E^ (-gamma) ph cm^(-2) s^(-1) keV^(-1) ,\nover the 0.6-6 keV range, with A = 0.00051, and gamma = 1.75\n\nThus, the mean flux for the 0.6 to 6 keV band over the duration of \nthe Chandra observation was ~2.2 x 10^(-12) ergs cm^(-2) s^(-1).\n\nOur analyses are continuing, and more detailed results will be posted at:\n\nhttp://space.mit.edu/HETE/\n\nWe thank Harvey Tananbaum for his generous allocation of Director's \nDiscretion Time to this observation, and the Chandra X-ray \nObservatory Operations personnel for the impressive promptness with \nwhich this observation was planned and carried out.\n\nThe preliminary results reported here may be cited.",
  "circularId": 1504,
  "createdOn": 1029724209000,
  "email": "grr@space.mit.edu",
  "subject": "GRB020813: Fading X-ray Afterglow Observed with Chandra",
  "submitter": "George Ricker at MIT  <grr@space.mit.edu>",
  "eventId": "GRB 020813"
}