The Chandra High Energy Transmission Grating Spectrometer Probes the Dusty Warm Absorber in the Seyfert 1 Galaxy Mcg–6-30-15

The Chandra HETGS spectra of the Seyfert 1 galaxy MCG–6-30-15 show numerous narrow, unresolved (FWHM ∼ < 200 km s −1) absorption lines from a wide range of ionization states of N, O, Mg, Ne, Si, S, Ar, and Fe. The initial analysis of these data, presented in Lee et al. (2001), shows that a dusty warm absorber model adequately explains the spectral features ∼ > 0.48 keV (∼ < 26Å). We attribute previous reports of an apparently highly redshifted O vii edge to the neutral Fe L absorption complex and the O vii resonance series (by transitions higher than He γ; He α, β, γ are also seen at lower energies). The implied dust column density needed to explain the Fe i L edge feature agrees with that obtained from earlier reddening studies, which had already concluded that the dust should be associated with the ionized absorber (given the relatively lower observed X-ray absorption by cold gas). Our findings contradict the interpretation of Branduardi-Raymont et al. (2001), based on XMM-Newton RGS spectra, that this spectral region is dominated by highly relativistic soft X-ray line emission originating near the central black hole. Here we review these issues pertaining to the soft X-ray spectral features as addressed by Lee et al.