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N. J. Schurch, R. E. Griffiths (CMU)
Studies of the physical properties of 'intermediate' active galactic nuclei are intriguing because of their potential to test, and impact on, the the standard unification models of active galactic nuclei (AGN). In particular, the unique 'glancing' viewing angle implied in these objects highlights that they are the best, and possibly the only, sources that allow us to study both the high column density, relatively low ionization, absorbing material that may form the 'skin' of the molecular torus or the material immediately interior to the torus. The Seyfert 1.5 galaxy Markarian 6 (Mrk 6) was first identified as an intermediate Seyfert through optical spectroscopy by Osterbrock & Koski (1976) and is often referred too as a ''4151 analogue''. The comparison of the two recent XMM-Newton observations of Mrk 6 reveals that whilst the original observation revealed complex heavy column density absorption (~1023 cm-1), similar to that of NGC 4151, the most recent observation shows almost an order of magnitude less absorption. The similar ionizing luminosities in the two observations largely rules our significant absorption variability through ionization and is strong evidence in favor of a patchy structure for the absorbing material. A further degree of complexity is possible if the patchy material of the absorber is also partially ionized. Future observations of heavy, complex absorption in bright, nearby sources, particularly with Astro-EII, have the potential to distinguish between a patch neutral and patchy partially ionized absorption in similar sources.
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Bulletin of the American Astronomical Society, 36 #3
© 2004. The American Astronomical Soceity.