Soft X-ray properties of a complete sample of QSOs

Abstract

In order to study systematically the soft X-ray emission of AGNs, we have analyzed ROSAT PSPC spectra of 22 QSOs. The QSOs form a complete sample with soft X-ray flux ??1.4 x 10-14 erg cm-2 s-1 in the energy band of 0.1-2.0 keV in a circular region of radius 15 arcmin in the sky. The highest redshift QSO in the sample has z = 3.4. The average photon index (?) of the QSOs is 2.39 with a dispersion of 0.57. There are only 3 QSOs with ?x ??3.0. The average slope of the soft X-ray spectra of the QSOs flattens at higher redshifts. Only three out of 22 QSOs show the presence of a significant excess absorption over the Galactic value.