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|Title:||Serendipitous active galactic nuclei in the XMM–Newton fields of Markarian 205 and QSO 0130−403|
|Authors:||Page, Kim L.|
Turner, Martin J. L.
Reeves, J. N.
O'Brien, Paul T.
|Publisher:||Oxford University Press (OUP) on behalf of the Royal Astronomical Society|
|Citation:||Monthly Notices of the Royal Astronomical Society, 2003, 338 (4), pp. 1004-1012|
|Abstract:||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[superscript 44] erg s[superscript −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[subscript 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 αox 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[subscript 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.|
|Appears in Collections:||Published Articles, Dept. of Physics and Astronomy|
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