Iron Line Spectroscopy of NGC 4593 with XMM-Newton:
Where is the Black Hole Accretion Disk?

$^1$Dept. of Astronomy, University of Maryland, College Park, MD 20742, USA.
$^2$Institut für Astronomie und Astrophysik, Abt. Astronomie, Universität Tübingen, Sand 1, 72076 Tübingen, Germany
$^3$Department of Physics, University of Warwick, Coventry, CV4 7AL
$^4$Dept. of Physics and Astronomy, Johns Hopkins University, 3400 Charles Street, Baltimore, MD 21218.

In press

Abstract:

We present an analysis of the 2-10keV XMM-Newton/EPIC-pn spectrum of the Seyfert-1 galaxy NGC 4593. Apart from the presence of two narrow emission lines corresponding to the K$\alpha$ lines of cold and hydrogen-like iron, this spectrum possesses a power-law form to within $\sim 3-5\%$. There is a marked lack of spectral features from the relativistic regions of the black hole accretion disk. We show that the data are, however, consistent with the presence of a radiatively-efficient accretion disk 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.