The Fifth Data Release Sloan Digital Sky Survey/ XMM-Newton Quasar Survey

We present a catalog of 792 Fifth Data Release Sloan Digital Sky Survey quasars with optical spectra that have been observed serendipitously in the X-rays with the XMM-Newton . These quasars cover a redshift range of z = 0.11–5.41 and a magnitude range of i = 15.3–20.7. Substantial numbers of radio-loud (70) and broad absorption line (51) quasars exist within this sample. Significant X-ray detections at ⩾2σ account for 87% of the sample (685 quasars), and 473 quasars are detected at ⩾6σ, sufficient to allow X-ray spectral fits. For detected sources, ∼60% have X-ray fluxes between F 2−10 keV = (1–10) × 10 −14 erg cm −2 s −1 . We fit a single power law, a fixed power law with intrinsic absorption left free to vary, and an absorbed power-law model to all quasars with X-ray signal-to-noise ratio ⩾ 6, resulting in a weighted mean photon index Γ = 1.91 ± 0.08, with an intrinsic dispersion σ Γ = 0.38. For the 55 sources (11.6%) that prefer intrinsic absorption, we find a weighted mean N H = 1.5 ± 0.3 × 10 21 cm −2 . We find that Γ correlates significantly with optical color, Δ( g − i ), the optical-to-X-ray spectral index (α ox ), and the X-ray luminosity. While the first two correlations can be explained as artifacts of undetected intrinsic absorption, the correlation between Γ and X-ray luminosity appears to be a real physical correlation, indicating a pivot in the X-ray slope.