SIMBAD references

We present X-ray spectral analyses of the three z>4 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 (~2 Ms) and the low Chandra background. The rest-frame ~2.5-40 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 Γ=1.8±0.3, consistent with those of lower-redshift, unobscured AGNs. The other two AGNs have flatter effective X-ray photon indices (Γ~1.1-1.5), 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~2x10²³ cm^–2.