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L. Rudnick, J. Ennis (Univ. of MN), W. Reach (SSC/Caltech), J. D. Smith (Univ. of AZ), J. Rho (SSC/Caltech), T. DeLaney (Harvard-Smithsonian Ctr. for Astrophysics), T. Kozasa (Hokkaido Univ.), H. Gomez (Cardiff Univ.)
We present Spitzer IRAC images of the supernova remnant Cassiopeia A, supplemented by data from the IRS, along with MIPS and near infrared images. We find that the IRAC bands each present a different view of Cas A, and highlight different layers of the explosion. IRAC Channel 1 contains a significant contribution from synchrotron radiation. It dominates over the other IRAC channels in the outer shock region. IRS spectra of bright Channel 1 regions show a broad peak around 26 microns, likely from shock heated circumstellar/interstellar dust. IRAC Channel 4 dominates the other IRAC channels where [ArII] is strong, and shows the same structures as Ar maps from IRS at 7 and 8.9 microns. These structures are similar to those seen in the optical and X-ray. IRS spectra of bright Channel 4 regions also show a sharp peak around 21 microns, likely caused by dust from the O- and Si- burning layers. Where [ArII] is weak, IRAC Channels 2 or 3 are stronger relative to Channel 4. In those regions, the IRS spectra rise gradually and then flatten longward of 23 microns, without a 21 micron peak. In the interior, we see emission from [SiII] and [SIII]. All these findings appear consistent with the idea that in each direction different nucleosynthetic layers have reached the reverse shock.
This work was performed for the Jet Propulsion Laboratory, California Institute of Technology, sponsored by the United States Government under Prime Contract between California Institute of Technology and NASA.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.