A Compton-thin solution for the Suzaku X-ray spectrum of the Seyfert 2 galaxy Mkn 3

Abstract

Mkn 3 is a Seyfert 2 galaxy that is widely regarded as an exemplary Compton-thick Active Galactic Nucleus (AGN). We study the Suzaku X-ray spectrum using models of the X-ray reprocessor that self-consistently account for the Fe Kα fluorescent emission line and the associated Compton-scattered, or reflection, continuum. We find a solution in which the average global column density, 0.234^{+0.012}_{-0.010} × 10^{24} cm^{-2}, is very different to the line-of-sight column density, 0.902^{+0.012}_{-0.013} × 10^{24} cm^{-2}. The global column density is ∼5 times smaller than that required for the matter distribution to be Compton thick. Our model accounts for the profiles of the Fe Kα and Fe Kβ lines, and the Fe K edge remarkably well, with a solar abundance of Fe. The matter distribution could consist of a clumpy medium with a line-of-sight column density higher than the global average. A uniform, spherically symmetric distribution alone cannot simultaneously produce the correct fluorescent line spectrum and reflection continuum. Previous works on Mkn 3, and other AGN, that assumed a reflection continuum from matter with an infinite column density could therefore lead to erroneous or `puzzling' conclusions if the matter out of the line of sight is really Compton thin. Whereas studies of samples of AGN have generally only probed the line-of-sight column density, with simplistic, one-dimensional models, it is important now to establish the global column densities in AGN. It is the global properties that affect the energy budget in terms of reprocessing of X-rays into infrared emission, and that constrain population synthesis models of the cosmic X-ray background.