Probing circumnuclear material in Seyfert galaxies with X-ray spectroscopy.

摘要

Using archival X-ray observations of Seyfert galaxies, we test the limits of the unified model for Seyfert galaxies. By considering the line-of-sight attenuating columns within the context of the relative arrangement of the Seyfert structural components, we find evidence suggesting that there are two distinct structures which are capable of absorbing the broad-line emission and giving rise to type 2 spectral characteristics. One absorbing system has high column densities (N_H > 1023 cm −2) and is uncorrelated with the orientation of the host galaxy, while the other has lower column densities and is more closely associated with the host galactic plane. In addition to establishing the presence of two discrete absorbing structures, we are able to place some constraints on the geometry of these structures.; In a separate survey of type 1 Seyferts with repeated observations in the ASCA archive, we find that variability of the iron line commonly occurs on a wide range of timescales, and is generally uncorrelated with changes in the continuum. The disappearance of the iron feature puts a strong upper limit on the contribution of large-scale structures to the line flux in some systems, raising the question of whether putative tori are present in all Seyfert galaxies. In addition, the lack of correlated variability is similar to results obtained for shorter timescales and is difficult to reconcile with simple models of reflection. Taken together, these results call into question both the completeness and the universality of the unified model for Seyfert galaxies.