We explore the X-ray properties of optically selected QSOs spectroscopically identified in the course of the 2dF QSO survey ( 2QZ ) .
Our main goal is to expand to higher redshifts previous findings suggesting the presence of a fraction of X-ray obscured sources among the low redshift optically selected broad line AGN population .
The X-ray data are from the wide field ( \sim 2.5 deg ^ { 2 } ) shallow [ f ( 0.5 - 8 keV ) \approx \times 10 ^ { -14 } erg~ { } cm ^ { -2 } ~ { } s ^ { -1 } ~ { } ] XMM- Newton /2dF survey .
A total of 96 2QZ QSOs overlap with the area covered by our X-ray survey .
66 of them have X-ray counterparts while 30 remain undetected in our X-ray survey .
The 66 X-ray detected QSOs have a mean photon index of \approx 2 suggesting little or no X-ray obscuration for most of these sources .
Individual X-ray spectral fittings reveal only 1 source ( intrinsic L _ { X } ( 0.5 - 8 ~ { } keV ) \sim 10 ^ { 44 } ~ { } erg~ { } s ^ { -1 } at z = 0.82 ) that is likely to be obscured ( N _ { H } \approx 10 ^ { 23 } cm ^ { -2 } ) at the 90 % confidence level .
Additionally , there are 9 2QZ sources that show evidence for moderate absorption ( mean observed N _ { H } of \approx 10 ^ { 21 } cm ^ { -2 } ) .
For the 30 QSOs that remain undetected in our X-ray survey we use stacking analysis to estimate a mean hardness ratio of -0.59 \pm 0.11 suggesting that the bulk of this population has N _ { H } consistent with the Galactic value .
However , we can not exclude the possibility that some of these sources have enhanced photoelectric absorption that is not revealed in the mean stacked spectrum .
We estimate a lower limit to the fraction of optically selected QSO with X-ray absorption of about 10 % ( 10 out of 96 ) .