The X-ray spectra of serendipitously observed AGN in the XMM-Newton fields of Mrk 205 and QSO 0130 - 403 are analysed .
The sample consists of 23 objects , none of which is detected at radio frequencies , with a median X-ray luminosity of \sim 4 \times 10 ^ { 44 } erg s ^ { -1 } and redshifts ranging from \sim 0.1 to just over 3 .
The mean photon index was found to be 1.89 \pm 0.04 .
In contrast to past ASCA and ROSAT observations of high-redshift radio-loud quasars , we find little evidence for excess intrinsic absorption in these radio-quiet objects , with only three sources requiring a column density in excess of the Galactic value .
Comparing the measured spectral indices over the redshift range , we also find there is no X-ray spectral evolution of QSOs with time , up to redshift 3 .
Within the sample there is no evidence for evolution of the optical to X-ray spectral index , \alpha _ { ox } , with redshift , the mean value being - 1.66 \pm 0.04 .
However , upon comparing the values from the Bright Quasar Survey at low redshift ( z < 0.5 ) and high redshift QSOs detected by Chandra ( z > 4 ) , a slight steepening of \alpha _ { ox } is noted for the more distant objects .
In most of the sources there is no significant requirement for a soft excess , although a weak thermal component ( \leq 10 per cent of L _ { X } ) can not be excluded .
There is an indication of spectral flattening ( by \Delta \Gamma = 0.2 ) at higher energies ( > 3 keV , QSO rest frame ) for the sample as a whole .
This is consistent with the presence of a Compton reflection component in these radio-quiet AGN , with the scattering medium ( such as an accretion disc or molecular torus ) occupying a solid angle of 2 \pi steradians to the X-ray source .