The soft X-ray absorption lines of the Seyfert 1 galaxy MCG-6-30-15

Abstract

The absorption lines in the soft X-ray spectrum of MCG-6-30-15 are studied using the reflection grating spectrometer data from the 2001 XMM-Newton 320-ks observation. A line search of the full time-averaged spectrum reveals 51 absorption lines and one emission line. The equivalent widths of the lines are measured and the majority of the lines identified. We find lines produced by a broad range of charge states for several elements, including almost all the charge states of oxygen and iron, suggesting a broad range of ionization parameters is present in the warm absorber. The equivalent widths of the lines are broadly consistent with the best-fitting warm absorber models from Turner et al. The equivalent widths of the absorption lines allow confidence limits on the column density of the species to be determined. For O VII, a column density of 1018.36-1018.86 cm-2 is found. This column density of O VII, when combined with the inferred Fe I absorption, is sufficient to explain the drop in flux at 0.7 keV as being due to absorption from the warm absorber. Fitting O I K-edge absorption to the spectrum reveals a column of 1017.51-1017.67 cm-2 of O I, suggesting an Fe:O ratio of ∼1:2, consistent with the neutral iron being in the form of iron oxide dust. Variability is seen in a few absorption lines, but the majority of the absorption features, including the prominent absorption edges, stay constant throughout the observation despite variability in the continuum flux.