Nucleosynthesis and mixing in Cassiopeia A

We present results from the first light observations of the Cassiopeia A su pernova remnant (SNR) by the Chandra X-Ray Observatory. Based on representa tive spectra from four selected regions, we investigate the processes of nu cleosynthesis and mixing in Cas A. We make the first unequivocal identifica tion of iron-rich ejecta produced by explosive silicon burning in a young G alactic SNR. Elsewhere in the remnant, we see silicon rich ejecta from expl osive oxygen burning. The Fe-rich ejecta lie outside the Si-rich material, indicating that bulk motions were extensive and energetic enough in Cas A t o 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 i n plumes from the rising bubbles in the neutrino-driven convection layer du ring the supernova explosion. In addition, the radioactive decay energy fro m Ni-56 may have contributed to the subsequent evolution of the material. W e have also discovered faint, well-defined filaments with featureless X-ray spectra that are possibly sites of cosmic-ray acceleration in Cas A.