shows, the sector of the radial profile encompassing the bright northwestern arc exhibits a $7.8\sigma$ excess between semi-minor axis radii of $13.5^{\prime\prime}$ and $18.0^{\prime\prime}$ in the sense that the source is brighter in the second observation. No other sectors or radii show any significant changes. In Figure 7, we display the azimuthal profile of the whole nebula in the elliptical ring $4.5^{\prime\prime}$ wide centered on these radii. The residuals are positive (the second observation is brighter) throughout the range $250^\circ$ to $30^\circ$; the excess is significant at the $7.6 \sigma$ level and represents a brightening of 5.3%. The excess energy being radiated in the HRC band amounts to $\sim 3 \times 10^{30}$ erg s$^{-1}$. For the assumed geometry discussed in $\S 6.1$, the outer arc lies at a distance of $1.05 \times 10^{17}$ cm from the pulsar, requiring signal propagation at $\simgt 0.7c$ if the impetus for the brightening originated from the pulsar at the time of the glitch.

Discussion
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Geometry and Kinematics of the Nebular Structure
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Figure 8 shows our proposed model for the Vela X-ray nebula. We assume that the two prominent arc-like features lie along circular rings highlighting shocks in which the energy of an 