X-Ray Study of the Distant QSO PKS 0237–233 with ASCA and ROSAT

Abstract

The X-ray spectrum of the distant QSO PKS 0237–233 (z = 2.223) has been studied with ASCA and ROSAT. The spectrum in the energy range 0.1 keV to 8 keV in the observer's frame is well fitted by a power-law model with a photon index of 1.54 ± 0.06 absorbed by the galactic interstellar matter. The lack of excess absorption confirms that such absorption is not a universal property of the high-redshift GHz-peaked spectrum (GPS) sources. From a comparison of the Lyman alpha and the metal absorption lines in the optical and UV bands, small amount of X-ray absorption constrains the ionization state of the metal line system at z = 1.65 as [HI/H] > 2.5 × 10−4 and [CIV/C] > 0.11 if the metal line systems have a metal abundance of 0.1Z⊙.