The X-ray variability of high redshift QSOs

We present an analysis of X-ray variability in a sample of 156 radio quiet quasars taken from the ROSAT archive, covering a redshift range 0.1 2) in the sense that QSOs of the same X-ray luminosity are more variable at z > 2. We discuss possible explanations for this effect. The simplest explanation may be that high redshift QSOs are accreting at a larger fraction of the Eddington limit than local AGN