contrast of $3,000$ for Cas A.

Filaments and SN Ejecta
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### Shock Parameters of the -SE filament

The filaments are located within the bright SNR shell in contrast to the filaments. The -SE filament has a remarkable correlation with the radio shell in both morphology and brightness. The knotty emission features inside the remnant might be within the shell too, but projected on the sky. The location of the filaments suggests that the emission is almost certainly from the shocked gas. The shock must be radiative and the emission should originate from the cooling layer behind the shock.

The -SE filament is very bright with the dereddened 164 peak surface brightness of $1.80 \pm 0.18\times 10^{-2}$ ergs cm$^{-2}$ s$^{-1}$ sr$^{-1}$. It is in fact the brightest among the known 164 filaments associated with SNRs. The total dereddened 164 flux is $1.0\pm 0.1 \times 10^{-10}$ erg cm$^{-2}$ s$^{-1}$. The ratio of 164 to line ($\sim 80$) toward the peak position of the -SE filament is larger or comparable to the ratios observed in other SNRs, e.g., 27 to $\ge 71$ in IC 443 [@gra87] or 34 in RCW 103 [@oli89]. It was pointed out in previous studies that the high 