Finding Rare AGN: XMM-Newton and Chandra Observations of SDSS Stripe 82
  We have analyzed the {\it XMM-Newton} and {\it Chandra} data overlapping
$\sim$16.5 deg$^2$ of Sloan Digital Sky Survey Stripe 82, including $\sim$4.6
deg$^2$ of proprietary {\it XMM-Newton} data that we present here. In total,
3362 unique X-ray sources are detected at high significance. We derive the {\it
XMM-Newton} number counts and compare them with our previously reported {\it
Chandra} Log$N$-Log$S$ relations and other X-ray surveys. The Stripe 82 X-ray
source lists have been matched to multi-wavelength catalogs using a maximum
likelihood estimator algorithm. We discovered the highest redshift ($z=5.86$)
quasar yet identified in an X-ray survey. We find 2.5 times more high
luminosity (L$_x \geq 10^{45}$ erg s$^{-1}$) AGN than the smaller area {\it
Chandra} and {\it XMM-Newton} survey of COSMOS and 1.3 times as many identified
by XBo\"otes. Comparing the high luminosity AGN we have identified with those
predicted by population synthesis models, our results suggest that this AGN
population is a more important component of cosmic black hole growth than
previously appreciated. Approximately a third of the X-ray sources not detected
in the optical are identified in the infrared, making them candidates for the
elusive population of obscured high luminosity AGN in the early universe.
