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Published December 20, 2010 | Published
Journal Article Open

The Three-Dimensional Structure of Interior Ejecta in Cassiopeia A at High Spectral Resolution

Abstract

We used the Spitzer Space Telescope's Infrared Spectrograph to create a high-resolution spectral map of the central region of the Cassiopeia A (Cas A) supernova remnant, allowing us to make a Doppler reconstruction of its three-dimensional structure. The ejecta responsible for this emission have not yet encountered the remnant's reverse shock or the circumstellar medium, making it an ideal laboratory for exploring the dynamics of the supernova explosion itself. We observe that the O, Si, and S ejecta can form both sheet-like structures and filaments. Si and O, which come from different nucleosynthetic layers of the star, are observed to be coincident in velocity space in some regions, and separated by 500 km s^(–1) or more in others. Ejecta traveling toward us are, on average, ~900 km s^(–1) slower than the material traveling away from us. We compare our observations to recent supernova explosion models and find that no single model can simultaneously reproduce all the observed features. However, models of different supernova explosions can collectively produce the observed geometries and structures of the interior emission. We use the results from the models to address the conditions during the supernova explosion, concentrating on asymmetries in the shock structure. We also predict that the back surface of Cas A will begin brightening in ~30 years, and the front surface in ~100 years.

Additional Information

© 2010 American Astronomical Society. Received 2009 August 12; accepted 2010 May 31; published 2010 December 3. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under NASA contract 1407. This work was supported in part by NASA/SAO Award AR5–6008X and NASA/JPL through award 1265552 to the University of Minnesota. K.I. thanks Alex Heger for valuable conversations concerning supernova explosion physics. K.I. also thanks Kris Eriksen for his insights concerning photoionization models of the interior emission in Cas A. We also appreciate the useful comments of the referee.

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