Before leaving MCG-6-30-15, we will briefly discuss a fascinating debate that is currently raging about the soft X-ray spectrum of this object. The soft X-ray spectrum of this, and many other type-1 AGN, is rather complex. Prior to the launch of XMM-Newton, it was widely accepted that this complexity was due to absorption by photoionized material along the line of sight to the central engine (the so-called warm absorber; [221,222]), with the principal observables being the photoelectric absorption edges of OVII and OVIII. In many objects, this hypothesis has been confirmed by high-resolution grating spectroscopy with Chandra and XMM-Newton; such spectra clearly display the resonant absorption lines of oxygen that are expected to accompany the photoelectric edges (e.g., see the fabulous X-ray spectrum of NGC 3783 obtained by Kaspi and collaborators; [223]). However, in MCG-6-30-15, an XMM-Newton grating spectrum showed that the simple warm absorber model fails -- there are anomalous ``edges'' and an apparant lack of strong oxygen resonance absorption lines [224]. On the basis of this, Branduardi-Raymont and collaborators suggested that the soft X-ray spectral complexity is due to strong, relativistically broadened oxygen, nitrogen and carbon recombination lines rather than a warm absorber [224]. The team led by Julia Lee analysing the non-simultaneous Chandra grating data can, however, explain the soft X-ray spectrum in terms of a warm absorber which contains embedded iron-rich dust [225]. It remains unclear whether the dusty warm absorber model can explain the XMM-Newton grating data.
Given the rapid and on-going development of these arguments (both for and against the idea of soft X-ray recombination lines that possess relativistic disk profiles), we refrain from drawing conclusions at this time. The interested reader is pointed to the astrophysical literature on X-ray spectroscopy of MCG-6-30-15.