  We report on spectral and timing properties of the magnetar CXOU
J164710.2-455216 in the massive star cluster Westerlund 1. Using 11 archival
observations obtained with Chandra and XMM-Newton over approximately 1000 days
after the source's 2006 outburst, we study the flux and spectral evolution of
the source. We show that the hardness of the source, as quantified by hardness
ratio, blackbody temperature or power-law photon index, shows a clear
correlation with the 2--10 keV absorption-corrected flux and that the power-law
component flux decayed faster than the blackbody component for the first ~100
days. We also measure the timing properties of the source by analyzing data
spanning approximately 2500 days. The measured period and period derivative are
10.610644(17) s (MJD 53999.06) and <4 X 10^{-13} s s^-1 (90% confidence) which
imply that the spin-inferred dipolar magnetic field of the source is less than
7 X 10^{13} G. This is significantly smaller than was suggested previously. We
find evidence for a second flux increase, suggesting a second outburst between
MJDs 55068 and 55832. Finally, based on a crustal cooling model, we find that
the source's cooling curve can be reproduced if we assume that the energy was
deposited in the outer crust and that the temperature profile of the star right
after the 2006 outburst was relatively independent of density.
