Serendipitous active galactic nuclei in the XMM–Newton fields of Markarian 205 and QSO 0130−403

The X‐ray spectra of serendipitously observed active galactic nuclei (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 ∼4 × 10 44 erg s −1 and redshifts ranging from ∼0.1 to just over 3. The mean photon index was found to be 1.89 ± 0.04 . In contrast with 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 quasi‐stellar objects (QSOs) with time, up to redshift of 3. Within the sample there is no evidence for evolution of the optical to X‐ray spectral index, α ox , with redshift, the mean value being −1.66 ± 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 α 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 (≤10 per cent of L X ) cannot be excluded. There is an indication of spectral flattening (by ΔΓ= 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 2π sr to the X‐ray source.