2005ApJ...629L..17R

We have searched in the XMM-Newton public archive for quasars in the Sloan Digital Sky Survey First Data Release and found 55 lying in the field of an XMM-Newton observation with exposure times >20 ks (as of 2004 August). The 35 quasars that yielded good X-ray spectra span redshifts from 0.5 to 2.5. The large collecting area of XMM-Newton allows us to investigate the dependence of the X-ray spectra of quasars on luminosity, redshift, and optical colors. We find (1) no evolution of X-ray slope (Γ) with either redshift or luminosity; (2) no correlation between Γ (or absorbing column density) and the optical-to-X-ray ratio, α_OX; and (4) no relation between α_OX and optical colors. The two latter results suggest that obscuration is not the dominant cause of the spread in X-ray slope or optical color. We find four unusual quasars (i.e., 10% of the sample): three are absorbed (N_H>10²²/cm2), of which one has high luminosity (1.5x10⁴⁴ ergs/s); the fourth has Γ=0.6±0.2, which is far flatter than the typical value of 1.8-2.0, and a strong emission line (EW=1.2±0.4 keV), which, if Fe K, implies a redshift of ∼1.4.