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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, xs, and of the fractional rms variability amplitude, fvar. The scatter in 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 xs and fvar, reducing the fluctuations of the individual variances, chang e with time, indicating non-stationary variability. Moreover, both the averaged sqxs (absolute rms variability amplitude) and fvar show linear correlation with source flux but in an opposite sense: sqxs correlates with flux, but fvar anti-correlates with flux. These correlations suggest that the variability process of the source is strongly non-stationary as random scatters of variances should not yield any correlation. fvar spectra were constructed to compare variability amplitudes in different energy bands. We found that the fractional rms variability amplitude of the source, when significant variability is observed, increases logarithmically with the photon energy, indicating significant spectral variability. The point-to-point variability amplitude may also track this trend, suggesting that the slopes of the power spectral density of the source are energy-independent. Using the normalized excess variance the black hole mass of pks was estimated to be about $1.45 times 10^8 M_{bigodot}$. This is compared and contrasted with the estimates derived from measurements of the host galaxies.
With currently available XMM-Newton EPIC pn observations spanned over about 3 years, we present a detailed spectral and temporal variability of the 0.2--10 keV X-ray emission from the X-ray bright BL Lac object PKS 2155-304. The spectral variability
XMM observed the BL Lac PKS 2155-304 for a full orbit (about 150 ksec) on 2000 November 19-21. Preliminary results on the temporal and spectral analysis of data from the EPIC PN camera and Optical Monitor are presented. The variability amplitude depe
Studying the temporal variability of BL Lac objects at the highest energies provides unique insights into the extreme physical processes occurring in relativistic jets and in the vicinity of super-massive black holes. To this end, the long-term varia
The EPIC pn CCD camera on board of XMM-Newton is designed to perform high throughput imaging and spectroscopy as well as high resolution timing observations in the energy range of 0.1-15 keV. A temporal resolution of milliseconds or microseconds, dep
We have examined 13 pointed observations of the TeV emitting high synchrotron peak blazar PKS 2155-304, taken by the Suzaku satellite throughout its operational period. We found that the blazar showed large-amplitude intraday variabilities in the sof