Optically luminous QSOs observed with ROSAT.

We present ROSAT PSPC observations of six luminous high-redshift (z = 2.15 to 3.2) QSOs. All were detected in X-rays. For four of them with greater than or similar to 200 counts spectral fittings using power laws yield a photon index alpha(P) = 2.25 +/- 0.2 acid hydrogen column densities NH consistent with Galactic NH values. There is no evidence for excess absorption due to intervening matter, in agreement with Bechtold et al.'s (1994) findings for radio quiet QSOs, who also found a similar spectral index. HE1104-1805 (z = 2.303), the recently discovered bright double QSO (Wisotzki et al., 1993) is particularly X-ray loud (0.095 cts s(-1)) and radio quiet (<0.18 mJy at 6 cm). Our observations support the view that the apparent excess absorption found in several radio-loud high redshift QSOs is intrinsic to the objects and distinguishes them from radio quiet QSOs and from most low-redshift AGN which have no intrinsic absorption.