The Forward and Reverse Shock Dynamics of Cassiopeia A

We report on proper motion measurements of the forward- and reverse-shock regions supernova remnant Cassiopeia A (Cas A), including deceleration/acceleration forward shock. The combine 19 years observations with Chandra X-ray Observatory, using 4.2-6 keV continuum band, preferentially targeting synchrotron radiation. average expansion rate is $0.218 \pm 0.029$%yr$^{-1}$ for shock, corresponding to a velocity $\approx 5800$ km/s. time derivative motions indicates deceleration in east, an acceleration up $1.1\times 10^{-4}$ yr$^{-2}$ western part. reverse shock moves outward East, but West it toward center $-0.0225\pm 0.0007$ %yr$^{-1}$, $-1884\pm 17$ In ejecta frame $\gtrsim 3000$ km/s, peaking at $\sim 8000$ explaining presence emitting filaments there. backward can be explained by either scenario which encountered partial, dense, wind shell, or one transgressed initially through lopsided cavity, created during brief Wolf-Rayet star phase. Both scenarios are consistent local Finally we northeastern jet, both Si XIII K-line emission band. find rates respectively 0.21%yr$^{-1}$ 0.24%yr$^{-1}$, velocities tip jet 7830--9200