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We use recent collisional ionization models that allow us to correlate observed changes in spectrum with a rough estimate of when the Mg and Fe layers reached the reverse shock. These ejecta are then used to determine if the original nucleosynthetic layers of the star are arriving at Cas A’s reverse shock at different times. We identify the most recently shocked X-ray ejecta with ionization timescales of #24 1010 cm−3 s, nearly an order of magnitude smaller than previously identified shocked ejecta. We determine that this corrugation is likely caused during the supernova explosion itself, rather than hundreds of years later at the remnant’s reverse shock.įinally, we present a detailed multi-epoch X-ray analysis of Cas A using Chandra X-ray Observatory exposures from 2000, 2002, and 2004. Finally, we observe small-scale velocity structures in the recently shocked ejecta. We again compare these observations of the nucleosynthetic layers to predictions from supernova explosion models in an attempt to constrain such models. Si and O are observed to be coincident in some directions, but segregated by up to #24 500 km s−1 in other directions. We determine that the velocity width of the nucleosynthetic layers is #24 1000 km s−1 in a given region, although the velocity width of a layer along any given line of sight is <250 km s−1. We determine that the reverse shock of the remnant is spherical to within 7%, although the center of this sphere is offset from the geometric center of the remnant by 810 km s−1. In these regions, we observe supernova ejecta both immediately before and during the shock-ejecta interaction. We then used similar observations from 3 regions on Cas A’s reverse shock in order to create more 3-dimensional maps. We also predict that the back surface of Cassiopeia A will begin brightening in #24 30 years, and the front surface in #24 100 years. We use the results from the models to address the conditions during the supernova explosion, concentrating on asymmetries in the shock structure. However, models of different supernova explosions can collectively produce the observed geometries and structures of the emission interior to Cas A’s reverse shock. We compare our observations to recent supernova explosion models and find that no single model can simultaneously reproduce all the observed features. Observed ejecta traveling toward us are, on average, #24 800 km s−1 slower than the material traveling away from us. Si and O, which come from different nucleosynthetic layers of the star, are observed to be coincident in some regions, and separated by >500 km s−1 in others. These ejecta can form both sheet-like structures as well as filaments. In the center of the remnant, we find relatively pristine ejecta that have not yet reached Cas A’s reverse shock or interacted with the circumstellar environment. In order to accomplish these science goals, we used the Spitzer Space Telescope’s Infrared Spectrograph to create a high resolution spectral map of select regions of Cas A, allowing us to make a Doppler reconstruction of its 3-dimensional structure structure. Additionally, we can observe key processes in the interstellar medium as the ejecta from the initial explosion encounter Cas A’s powerful shocks. Easily resolvable supernova remnants such as Cas A provide a unique opportunity to test supernova explosion models. We present a multi-wavelength study of the nearby supernova remnant Cassiopeia A (Cas A).