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[10.10] On the Determination of Ejecta Structure and Explosion Asymmetry from the X-ray Knots of Cassiopeia A

J. M. Laming (Naval Research Laboratory), U. Hwang (GSFC/UMD)

We present a detailed analysis of X-ray spectra from individual ejecta knots in the supernova remnant Cassiopeia A. The spectra are fitted to give the electron temperature, T_e and (single) ionization age n_et. These quantities are compared with the predictions of self similar hydrodynamic models incorporating time dependent ionization and radiation losses, and Coulomb electron-ion equilibration behind the reverse shock for a variety of different ejecta density profiles described by a uniform density core and a power law envelope. We find that the ejecta close to the ``jet'' region in the NE, have a systematically shallower outer envelope than ejecta elsewhere in the remnant, and we interpret this as being due to more energy of the initial explosion being directed in this polar direction as opposed to equatorially. The degree of asymmetry we infer is at the low end of that modelled in asymmetric core-collapse simulations, and may be used to rule out highly asymmetric explosions, as have been suggested, for example, in connection with 44Ti nucleosynthesis. Work supported by Basic Research Funds of the Office of Naval Research.

Bulletin of the American Astronomical Society, 35#2
© 2003. The American Astronomical Soceity.