We presented X-ray observations in the 0.1-100 keV spectral band of 8 Seyfert 2 galaxies. The sources were selected from the Maiolino & Rieke (1995) Seyfert sample (limited in B magnitude of the host galaxy) according to their [OIII] flux, that should deliver a sample not biased against heavily absorbed nuclei on the pc scale. Also, we avoided sources already observed in former hard X-ray surveys, generally X-ray bright. As a result, most of the sources in our sample are relatively X-ray weak.
We detected all of our targets in the 2-10 keV range, and two of them also in the 20-100 keV range. Most of these X-ray weak AGNs are characterized by prominent iron lines (at 6.4-7 keV) and flat observed continua, indicating that they are powered by the same kind of engine that powers X-ray bright AGNs. However, these X-ray weak AGNs are characterized by larger EW(Fe K) and flatter observed continua.
All of these sources are absorbed by column densities larger than cm-2 along our line of sight. Most of them appear to be thick to Compton scattering with NH 1025 cm-2. In the latter cases the observed continuum can generally be ascribed to Compton reflection by cold material.
These findings support the unified model, and point to an average absorbing column density in Sy2s that is much higher than presumed on the basis of previous X-ray surveys. The latter result has important implications for the synthesis of the X-ray background.
Finally, in some of these sources there is indication that the soft
X-ray excess cannot be fully ascribed to starburst activity in the
host galaxy, and a significant fraction of it is probably related to
the active nucleus itself.
© European Southern Observatory (ESO) 1998
Online publication: September 17, 1998