A softer look at MCG-6-30-15 with XMM-Newton

Abstract

We present the analysis and first results from the Reflection Grating Spectrometer (RGS) during the 320-ks XMM-Newton observation of the Seyfert 1 galaxy MCG-6-30-15. The spectrum is marked by a sharp drop in flux at 0.7 keV which has been interpreted by Branduardi-Raymont et al. using RGS spectra from an earlier and shorter observation as the blue wing of a strong relativistic O VIII emission line and by Lee et al. using a Chandra spectrum as due to a dusty warm absorber. We find that the drop is well explained by the Fe I L 2,3 absorption edges and obtain reasonable fits over the 0.32-1.7 keV band using a multizone, dusty warm absorber model constructed using the photoionization code CLOUDY. Some residuals remain which could be due to emission from a relativistic disc, but at a much weaker level than from any simple model relying on relativistic emission lines alone. A model based on such emission lines can be made to fit if sufficient (warm) absorption is added, although the line strengths exceed those expected. In order to distinguish further whether the spectral shape is dominated by absorption or emission, we examined the difference spectrum between the highest and lowest flux states of the source. The EPIC pn data indicate that this is a power law in the 3-10 keV band which, if extrapolated to lower energies, reveals the absorption function acting on the intrinsic spectrum, provided that any emission lines do not scale exactly with the continuum. We find that this function matches our dusty warm absorber model well if the power law steepens below 2 keV. The soft X-ray spectrum is therefore dominated by absorption structures, with the equivalent width of any individual emission lines in the residuals being below approximately 30 eV.