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The incidence of Active Galactic Nuclei (AGN) with local environment is apotentially valuable probe of the mechanisms that trigger and provide fuel foraccretion onto supermassive black holes. While the correlation between AGNfraction and environment has been well-studied in the local universe, AGNfractions have been measured for relatively few dense environments at highredshift. In this paper we present a measurement of the X-ray AGN fraction inthe USS 1558-003 protocluster associated with the z=2.53 radio galaxy 4C-00.62.Our measurement is based on a 100ks Chandra observation, follow-up spectroscopyfrom the Multi-Object Double Spectrograph on the Large Binocular Telescope, andbroad and narrow band photometry. These data are sensitive to AGN more luminousthan $L_{X}>2\times10^{43}$ erg s$^{-1}$ in the rest-frame hard X-ray band(2-10 keV). We have identified two X-ray AGN at the redshift of USS 1558-003,one of which is the radio galaxy. We have determined that $2.0^{+2.6}_{-1.3}$%of the H$\alpha$ emitters in the protocluster are X-ray AGN. Unlike most otherhigh-redshift cluster progenitors studied with similar techniques, USS 1558-003does not have a significantly higher fraction of AGN than field galaxies atsimilar redshifts. This lower AGN fraction is inconsistent with the expectationthat the higher gas fractions at high redshift, combined with the high galaxydensities and modest relative velocities in protoclusters, should producehigher AGN fractions.

The Fraction of Active Galactic Nuclei in the USS 1558-003 Protocluster at z = 2.53