1997A&A...320..421S

The ROSAT PSPC spectrum of the high-redshift quasar PKS 2351-154 (z=2.671) shows absorption which is significantly larger than the Galactic value in the direction of the source. This absorption is variable on time scales of ≤1.5-years corresponding to 0.41-years in the quasar's rest frame. In addition, we find indications that absorbing material is located at high redshifts. Optical observations revealed a CIV system with z_abs≃z_em. We conclude that this CIV system is related to the variable X-ray absorption. The variations can be explained in terms of changes in the ionization state of the absorbing material. In that case, the CIV system could be variable, too, and it could be close to the active galactic nucleus itself.