The EXOSAT spectral survey of AGN

Results are presented from EXOSAT observations of 48 hard X-ray selected Seyfert type active galactic nuclei (AGN). These include all 30 of the emission line AGN in the Piccinotti sample. Combining EXOSAT LE and ME data has allowed us to obtain X-ray spectra over the broad energy range 0.1 – 10 keV. Spectra in the |$\sim2-10$| keV range are found to be well described by a simple power law, with a narrow distribution of spectral indices across the sample about a mean energy index α = 0.70. EXOSAT has also revealed a substantial number of sources with complex soft X-ray spectra. These include spectra with a second emission component at soft X-ray energies as well as sources with ‘leaky’ absorbing columns. Evidence that soft emission components occur in many Seyferts, together with detection of rapid variability in the soft component, provides quantitative support for an accretion disc model for AGN. Approximately half our sample of AGN show low-energy absorption attributable to substantial cold matter within the host galaxy. A few cases show evidence for column variability and reduced low-energy opacity (by photo-ionization). These results and the observed rarity of intrinsic absorption in the higher luminosity sources suggest the absorbing matter lies close to the central continuum source.