2005ApJ...629..686Z -
Astrophys. J., 629, 686-699 (2005/August-3)
XMM-Newton view of PKS 2155-304: characterizing the X-ray variability properties with EPIC pn.
ZHANG Y.H., TREVES A., CELOTTI A., QIN Y.P. and BAI J.M.
Abstract (from CDS):
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, σ2XS, and of the fractional rms variability amplitude, Fvar. The scatter in σ2XSand 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 σ2XSand Fvar, which reduce the fluctuations of the individual variances, also change with time, indicating nonstationary variability. Moreover, both the averaged σXS(absolute rms variability amplitude) and the averaged Fvarshow linear correlation with source flux, but in an opposite sense: σXScorrelates with flux, but Fvaranticorrelates with flux. These correlations suggest that the variability process of the source is strongly nonstationary, as random scatters of variances should not yield any correlation. Spectra of Fvarwere 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 2155-304 was estimated to be about 1.45x108 M☉. This is compared and contrasted with the estimates derived from measurements of the host galaxies.
Abstract Copyright:
∼
Journal keyword(s):
Galaxies: BL Lacertae Objects: General - Galaxies: BL Lacertae Objects: Individual: Alphanumeric: PKS 2155-304 - Galaxies: Active - Methods: Data Analysis - X-Rays: Galaxies
Simbad objects:
7
Full paper
View the references in ADS
To bookmark this query, right click on this link: simbad:2005ApJ...629..686Z and select 'bookmark this link' or equivalent in the popup menu