ChandraObservations of the Highest Redshift Quasars from the Sloan Digital Sky Survey

We present new Chandra observations of 21 z>4 quasars, including 11 sourcesat z>5. These observations double the number of X-ray detected quasars at z>5,allowing investigation of the X-ray spectral properties of a substantial sampleof quasars at the dawn of the modern Universe. By jointly fitting the spectraof 15 z>5 radio-quiet quasars (RQQs), including sources from the Chandraarchive, with a total of 185 photons, we find a mean X-ray power-law photonindex of Gamma=1.95^{+0.30}_{-0.26}, and a mean neutral intrinsic absorptioncolumn density of N_H<~6x10^{22} cm^{-2}. These results show that quasar X-rayspectral properties have not evolved up to the highest observable redshifts. Wealso find that the mean optical-X-ray spectral slope (alpha_ox) ofoptically-selected z>5 RQQs, excluding broad absorption line quasars, isalpha_ox=-1.69+/-0.03, which is consistent with the value predicted from theobserved relationship between alpha_ox and ultraviolet luminosity. Four of thesources in our sample are members of the rare class of weak emission-linequasars, and we detect two of them in X-rays. We discuss the implications ourX-ray observations have for the nature of these mysterious sources and, inparticular, whether their weak-line spectra are a consequence of continuumboosting or a deficit of high-ionization line emitting gas.Comment: 15 pages (emulateapj), 8 figures. Accepted by Ap