The messy environment of Mrk 6

In recent years it has become clear that understanding the absorption present in active galactic nuclei (AGN) is essential given its bearing on unification models. We present the most recent XMM–Newton observation of Mrk 6, with the goal of understanding the nature and origin of the complex absorption intrinsic to this source. X-ray spectral fitting shows that a simple warm absorption model provides an equally good statistical representation of the CCD data as a partial covering model. Furthermore, once the Reflection Grating Spectrometer (RGS) data are included in the spectral fitting, the simple warm absorber model provides a very good fit to the data, without increasing the complexity of the model, in contrast with the partial covering model which requires the addition of either a low-metalicity (<0.03 solar) thermal plasma or low-temperature blackbody emission in order to provide a similar quality fit. The warm absorber is also a considerably more natural way to explain the variability observed in the X-ray absorbing column density between the previous XMM–Newton observation and this one, requiring only a second, higher column density, higher ionization, absorber to be present during the previous XMM–Newton observation. In comparison, the partial covering models which requires moving, clumpy, material relatively close to the source that result in two distinct lines of sight, with separate absorbing columns that each vary considerably without any associated change in their covering fractions, in order to explain the observed variability. We associate the warm absorber either with an accretion disc wind with densities of ∼109 cm−3, or with an ionized ‘skin’ or atmosphere of the molecular torus with densities of ∼103–5 cm−3.

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