NONTHERMAL PAIR MODELS, REFLECTION, AND X-RAY SPECTRAL VARIABILITY OF ACTIVE GALAXIES

Standard nonthermal electron-positron pair cascades, including the effects of reflection from an accretion disk, can explain reasonably well the mean spectra of low-luminosity, Seyfert-type active galaxies. We test this model using the spectral variability observed by EXOSAT between 0.05 and 10 keV in five active galaxies: NGC 5548, 3C 120, 3C 273, NGC 7469, and MCG 2-58-22. We find that pair-reflection models fail to reproduce the full range of spectra observed, particularly very hard spectra with a strong soft X-ray excess. Either the pair-reflection model is not an accurate description of the emission process in these objects or extrinsic effects, such as enhancement of the reflection component and/or a partially ionized absorber with a large column density, are responsible for much of the observed spectral variability.