TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1624 SUBJECT: GRB021004 Chandra HETG Observations DATE: 02/10/11 17:25:49 GMT FROM: Fiona Harrison at CalTech M. Sako, F. A. Harrison report on behalf of the Caltech-NRAO collaboration: We report TOO observations of GRB021004 taken with the High-Energy Transmission Grating (HETG) on the Chandra X-ray observatory. Chandra observed the afterglow for a total exposure of 87 ksec, beginning at 8:55 UT on October 5, 20.5 hours after the burst. A preliminary reduction of the data shows a fading X-ray source at the position of the optical transient. The count rate decreased with time throughout the observation with a power law decay time slope of -1.0 +/- 0.2. The total HEG + MEG countrate is 0.018 counts sec^-1. The source is well-characterized by a power-law spectrum with photon index Gamma = 2.1 +/- 0.1, and flux normalization of 1.9 +/- 0.1 x 10^-4 photons cm^-2 s^-1 keV^-1 at 1 keV. There are no signs of excess absorption above the Galactic value. The corresponding mean 2 - 10 keV X-ray flux in the observed frame is 4.3 x 10^-13 erg cm^-2 s^-1. The 0th-order ACIS-S spectrum is consistent with that of the HETG, with an average count rate of 0.014 counts sec^-1. No obvious discrete features are detected in the spectrum. We note that the signal-to-noise ratio in this spectrum is a factor of two better than that of the GRB991216 spectrum obtained with the Chandra HETG, so that a line feature of similar strength to that reported for GRB991216 should have been detected. We thank Harvey Tananbaum for approving director's discretionary time for this observation, and the staff at the Chandra Science Center for skillfully implementing this rapid TOO observation.