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Utilizing 21 new Chandra observations as well as archival Chandra, ROSAT, andXMM-Newton data, we study the X-ray properties of a representative sample of 59of the most optically luminous quasars in the Universe (M_i~~-29.3 to -30.2)spanning a redshift range of z~~1.5-4.5. Our full sample consists of 32 quasarsfrom the Sloan Digital Sky Survey (SDSS) Data Release 3 (DR3) quasar catalog,two additional objects in the DR3 area that were missed by the SDSS selectioncriteria, and 25 comparably luminous quasars at z>~4. This is the largest X-raystudy of such luminous quasars to date. By jointly fitting the X-ray spectra ofour sample quasars, excluding radio-loud and broad absorption line (BAL)objects, we find a mean X-ray power-law photon index ofGamma=1.92^{+0.09}_{-0.08} and constrain any neutral intrinsic absorbingmaterial to have a mean column density of N_H<~2x10^{21} cm^{-2}. We find,consistent with other studies, that Gamma does not change with redshift, and weconstrain the amount of allowed Gamma evolution for the most-luminous quasars.Our sample, excluding radio-loud and BAL quasars, has a mean X-ray-to-opticalspectral slope of a_ox=-1.80+/-0.02, as well as no significant evolution ofa_ox with redshift. We also comment upon the X-ray properties of a number ofnotable quasars, including an X-ray weak quasar with several strong narrowabsorption-line systems, a mildly radio-loud BAL quasar, and a well-studiedgravitationally lensed quasar.

The X-ray Properties of the Most-Luminous Quasars from the Sloan Digital Sky Survey