New Insight into AGN by Combining Spectral and Timing Information

Abstract

A case is made for combining spectral and timing analysis of X-ray data in order to better understand the physics at work in Active Galactic Nuclei (AGN). In analysing X-ray light curves from long EXOSAT ME observations of a sample of AGN with a new technique (assuming a stochastic behaviour of the sources) we determine characteristic variability time constants and nd that there is a signi cant correlation with the 2 - 10 keV spectral index (K onig et al. 1997). This establishes a relationship between the photon index of the X-ray spectrum, T , and the fastness of the variability. Similar relations have been noted between T and the variability amplitude (Green et al. 1993, Fiore et al. 1998).