Nucleosynthesis and mixing in Cassiopeia A

We present results from the first light observations of the Cassiopeia A supernova remnant (SNR) by the Chandra X-Ray Observatory. Based on representative spectra from four selected regions, we investigate the processes of nucleosynthesis and mixing in Cas A. We make the first unequivocal identification of iron-rich ejecta produced by explosive silicon burning in a young Galactic SNR. Elsewhere in the remnant, we see silicon-rich ejecta from explosive oxygen burning. The Fe-rich ejecta lie outside the Si-rich material, indicating that bulk motions were extensive and energetic enough in Cas A to cause a spatial inversion of a significant portion of the supernova core. It is likely that this inversion was caused by "Fe"-rich ejecta emerging in plumes from the rising bubbles in the neutrino-driven convection layer during the supernova explosion. In addition, the radioactive decay energy from ⁵⁶Ni may have contributed to the subsequent evolution of the material. We have also discovered faint, well-defined filaments with featureless X-ray spectra that are possibly sites of cosmic-ray acceleration in Cas A.