On broad iron K <italic>α</italic> lines in seyfert 1 galaxies

The X-ray spectrum obtained by Tanaka et al. from a long observation of the active galaxy MCG–6–30–15 shows a broad iron Kα line skewed to low energies. The simplest interpretation of the shape of the line is that it is due to Doppler and gravitational redshifts from the inner parts of a disc about a massive black hole. Similarly, broad lines are evident in shorter observations of several other active galaxies. In this paper we investigate other line broadening and skewing mechanisms such as Comptonization in cold gas and Doppler shifts from outflows. We have also fitted complex spectral models to the data of MCG–6–30–15 to see whether the broad skewed line can be mimicked well by other absorption or emission features. No satisfactory mechanism or spectral model is found, thus strengthening the relativistic disc line model.

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