The Chandra Deep Field-North Survey.: XVI.: The X-ray properties of moderate-luminosity active galaxies at z>4

We present X-ray spectral analyses of the z > 4 three active galactic nuclei (AGNs) thus far spectroscopically identified in the Chandra Deep Field-North Survey, at redshifts of 5.186, 4.424, and 4.137. These analyses are made possible by the extremely deep exposure (approximate to2 Ms) and the low Chandra background. The rest-frame approximate to2.5-40 keV spectra are the first for optically faint (two of the three sources have I >24) z >4 AGNs. The z = 5.186 quasar is well fitted by a power-law model with photon index Gamma = 1.8 +/- 0.3, consistent with those of lower-redshift, unobscured AGNs. The other two AGNs have flatter effective X-ray photon indices (Gammaapproximate to1.1-1.5), suggesting the presence of intrinsic absorption (provided their underlying X-ray continua are similar to those of lower redshift AGNs). It is possible that the flat X-ray continuum of the z = 4.424 AGN is partially related to its radio loudness. If the z = 4.137 AGN suffers from X-ray absorption, the implied column density is N-H approximate to 2 x 10(23) cm(-2).