Iron line spectroscopy of NGC 4593 with XMM-Newton: where is the black hole accretion disc?

Abstract

We present an analysis of the 2-10 keV XMM-Newton/EPIC-pn spectrum of the Seyfert-1 galaxy NGC 4593. Apart from the presence of two narrow emission lines corresponding to the Kα lines of cold and hydrogen-like iron, this spectrum possesses a power-law form to within ~3-5 per cent. There is a marked lack of spectral features from the relativistic regions of the black hole accretion disc. We show that the data are, however, consistent with the presence of a radiatively efficient accretion disc extending right down to the radius of marginal stability if it possesses low iron abundance, an appropriately ionized surface, a very high inclination, or a very centrally concentrated emission pattern (as has been observed during the deep minimum state of the Seyfert galaxy MCG-6-30-15). Deeper observations of this source are required in order to validate or reject these models.