The Kinematic and Plasma Properties of X‐Ray Knots in Cassiopeia A from theChandraHETGS

We present high-resolution X-ray spectra from the young supernova remnant CasA using a 70-ks observation taken by the Chandra High Energy TransmissionGrating Spectrometer (HETGS). Line emission, dominated by Si and S ions, isused for high-resolution spectral analysis of many bright, narrow regions ofCas A to examine their kinematics and plasma state. These data allow a 3Dreconstruction using the unprecedented X-ray kinematic results: we deriveunambiguous Doppler shifts for these selected regions, with values rangingbetween -2500 and +4000 km/s. Plasma diagnostics of these regions, derived fromline ratios of resolved He-like triplet lines and H-like lines of Si, indicatetemperatures largely around 1 keV, which we model as O-rich reverse-shockedejecta. The ionization age also does not vary considerably over these regionsof the remnant. The gratings analysis was complemented by the non-dispersedspectra from the same dataset, which provided information on emission measureand elemental abundances for the selected Cas A regions. The derived electrondensity of X-ray emitting ejecta varies from 20 to 200 cm^{-3}. The measuredabundances of Mg, Si, S and Ca are consistent with O being the dominant elementin the Cas A plasma. With a diameter of 5 arcmin, Cas A is the largest sourceobserved with the HETGS to date. We, therefore, describe the technique we useand some of the challenges we face in the HETGS data reduction from such anextended, complex object.Comment: 26 pages, 16 figures, evised version (minor changes), accepted for publication in ApJ (Oct 20 2006