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I determine the expansion of the supernova remnant of SN1604 (Kepler'ssupernova) based on archival Chandra ACIS-S observations made in 2000 and 2006.The measurements were done in several distinct energy bands, and were made forthe remnant as a whole, and for six individual sectors. The average expansionparameter indicates that the remnant expands as $r \propto t^{0.5}$, but thereare significant differences in different parts of the remnant: the brightnorthwestern part expands as $r \propto t^{0.35}$, whereas the rest of theremnant's expansion shows an expansion $r \propto t^{0.6}$. The latter isconsistent with an explosion in which the outer part of the ejecta has anegative power law slope for density ($\rho \propto v^{-n}$) of $n=7$, or withan exponential density profile($\rho \propto \exp(-v/v_e)$). The expansionparameter in the southern region, in conjunction with the shock radius,indicate a rather low value (<5E50 erg) for the explosion energy of SN1604 fora distance of 4 kpc. An higher explosion energy is consistent with the results,if the distance is larger.  The filament in the eastern part of the remnant, which is dominated by X-raysynchrotron radiation seems to mark a region with a fast shock speed $r \proptot^{0.7}$, corresponding to a shock velocity of v= 4200 km/s, for a distance toSN1604 of 4 kpc. This is consistent with the idea that X-ray synchrotronemission requires shock velocities in excess of ~2000 km/s.  The X-ray based expansion measurements reported are consistent with resultsbased on optical and radio measurements, but disagree with previous X-raymeasurements based on ROSAT and Einstein observations.

The Kinematics of Kepler's Supernova Remnant as revealed by Chandra