XMM-Newton View of PKS 2155–304: Characterizing the X-ray Variability Properties with EPIC-PN

Starting from XMM-Newton EPIC-PN data, we present the X-ray variability characteristics of PKS 2155–304 using a simple analysis of the excess variance, σ XS, and of the fractional rms variability amplitude, Fvar. The scatter in σ 2 XS and Fvar, calculated using 500 s long segments of the light curves, is smaller than the scatter expected for red noise variability. This alone does not imply that the underlying process responsible for the variability of the source is stationary, since the real changes of the individual variance estimates are possibly smaller than the large scatters expected for a red noise process. In fact the averaged σ XS and Fvar, reducing the fluctuations of the individual variances, change with time, indicating non-stationary variability. Moreover, both the averaged σXS (absolute rms variability amplitude) and Fvar show linear correlation with source