X-ray dependencies on luminosity in AGN

Abstract

Several X-ray properties of active galactic nuclei depend, or appear to depend, on their luminosity. It has long been suggested that alpha o-x, the X-ray ``loudness'' decreases with luminosity. There never has been a satisfactory explanation of this observational claim, and the statistical soundness of the result has been disputed. The earliest systematic studies of the X-ray variability of AGN showed that these properties also depend on luminosity. In particular, the normalization of the power spectrum, or alternatively the the variability amplitude, are anti-correlated with luminosity. Most recently, tentative evidence from Ginga for an X-ray Baldwin effect - a decrease in the iron K-alpha equivalent width with luminosity - has been confirmed and extended by ASCA. The new data show that the reduction in strength is accompanied by changes in profile. These results will be described and their interpretation discussed.