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Title: Can the soft excess in AGN originate from disc reflection?
Authors: Done, C.
Nayakshin, S.
First Published: 1-May-2007
Publisher: Royal Astronomical Society (RAS)
Citation: Monthly Notices of the Royal Astronomical Society: LETTERS, 2007, 377 (1)
Abstract: The soft excess seen in many active galactic nuclei (AGN) is most probably due to partially ionized material moving at relativistic speeds close to the black hole. There are currently two potential geometries for this material, one where it is out of the line of sight, seen via reflection (e.g. the accretion disc), the other where it is in the line of sight, seen in absorption (e.g. a wind above the disc). Both models require apparent fine-tuning of the ionization parameter of this material in order to produce the large jump in opacity at ∼0.7 keV associated with O vii/viii, as required to make the soft excess. However, Chevallier et al. show that these states rather naturally dominate the absorption spectrum for soft X-ray spectra if the illuminated material is (at least approximately) in pressure balance. Here we explore whether hydrostatic pressure equilibrium in a disc can likewise naturally select the required ionization states in reflection. We find the opposite. The soft excess X-ray excess is much weaker in the hydrostatic models than it is in the constant density models. Because even the constant density models cannot fit the largest soft excesses seen without the intrinsic continuum being hidden from view, this means that reflection from a hydrostatic disc cannot realistically match the data. Even if the disc structure is instead more like a constant density atmosphere, the required fine-tuning of the ionization parameter still remains a problem for reflection models.
DOI Link: 10.1111/j.1745-3933.2007.00303.x
ISSN: 1745-3933
Version: Publisher Version
Status: Peer-reviewed
Type: Journal Article
Rights: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2007 the authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. Deposited with reference to the publisher’s archiving policy available on the SHERPA/RoMEO website.
Appears in Collections:Published Articles, Dept. of Physics and Astronomy

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