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We present an updated catalog of X-ray point sources in the inner500$\arcsec$ ($\sim$20 parsec) of the Galactic Center (GC), where the {\itnuclear star cluster} (NSC) stands, based on a total of $\sim$4.5 Ms of {\itChandra} observations taken from September 1999 to April 2013. This ultra-deepdataset offers unprecedented sensitivity for detecting X-ray sources in the GC,down to an intrinsic 2--10 keV luminosity of$1.0\times10^{31}{\rm~erg~s^{-1}}$. A total of 3619 sources are detected in the2--8 keV band, among which $\sim$3500 are probable GC sources and $\sim$1300are new identifications. The GC sources collectively account for $\sim$20\% ofthe total 2--8 keV flux from the inner 250$\arcsec$ region where detectionsensitivity is the greatest. Taking advantage of this unprecedented sample offaint X-ray sources that primarily traces the old stellar populations in theNSC, we revisit global source properties, including long-term variability,cumulative spectra, luminosity function and spatial distribution. Based on theequivalent width and relative strength of the iron lines, we suggest that inaddition to the arguably predominant population of magnetic cataclysmicvariables (CVs), non-magnetic CVs contribute substantially to the detectedsources, especially in the lower-luminosity group. On the other hand, the X-raysources have a radial distribution closely following the stellar massdistribution in the NSC, but much flatter than that of the known X-raytransients, which are presumably low-mass X-ray binaries (LMXBs) caught inoutburst. This, together with the very modest long-term variability of thedetected sources, strongly suggests that quiescent LMXBs are a minor($\lesssim$ a few percent) population.

An Ultra-deep Chandra Catalog of X-ray Point Sources in the Galactic Center Star Cluster