X-ray spectra of active galactic nuclei

A study of active galactic nuclei using the Einstein Monitor Proportional Counter (MPC) is described. The MPC data analysis methods are described, including calibration, background subtraction, and spectral analysis. Spectral parameters in the 1-10 keV range are derived for 38 Seyfert or N galaxies and 14 QSOs which exceed a 2-10 keV flux limit of approx. = 9 x 10-12 erg cm-2 s-1. The mean power law energy index [α] is 0.68 +/- 0.05 for the sample as a whole, with no significant dependence on luminosity or classification (Seyfert or QSO). The rms dispersion in α is 0.31, which is due both to measurement errors and real differences in spectral index. Absorbing columns of > 1022 cm-2 are common among low luminosity (L/sub x/ < 1044 erg s-1) Seyfert galaxies, but relatively rare among higher luminosity objects. The low energy imaging instruments on Einstein are used in conjunction with the MPC to measure smaller column densities or soft excesses in several objects. The MPC data also reveal the ubiquity of variability on timescales of days to months, with lower luminosity Seyferts displaying the largest excursions. Several cases of variable column density have been found. The X-ray spectral results are discussed in terms of the synchrotron self-Compton mechanism and the nonthermal radio spectra which have similar power law indices of approx. = 0.7. The column densities are examined in terms of models for the optical emission line regions, and alternative models in which the X-ray flux actively regulates the ionization structure of a warmer medium. A generalized photoionization code has been developed with particular attention to X-ray effects and recent atomic data