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What is the origin of the soft excess in active galactic nuclei ?

Sobolewska, M. A. and Done, C. (2007) 'What is the origin of the soft excess in active galactic nuclei ?', Monthly notices of the Royal Astronomical Society., 374 (1). pp. 150-158.


We investigate the nature of the soft excess below 1 keV observed in active galactic nuclei. We use the XMM–Newton data of the low-redshift, optically bright quasar, PG 1211+143, and we compare it with the narrow-line Seyfert 1 galaxy, 1H 0707−495, which has one of the strongest soft excesses seen. We test various ideas for the origin of the soft X-ray excess, including a separate spectral component (for example, low-temperature Comptonized emission), a reflection-dominated model, or a complex absorption model. All three can give good fits to the data, and χ2-fitting criteria are not sufficient to discriminate among them. Instead, we favour the complex absorption model on the grounds that it requires less extreme parameters. In particular, the geometry appears to be more physically plausible as the reflected component in the smeared absorption model is no longer dominant, and relativistic distortions, while still clearly present, are not tremendously larger than expected for a disc around a Schwarzchild black hole.

Item Type:Article
Keywords:Accretion, accretion discs; Atomic processes, Galaxies: active; Galaxies: individual: PG 1211+143; Galaxies: individual: 1H 0707−495; X-rays: galaxies.
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Publisher statement:This article has been accepted for publication in Monthly notices of the Royal Astronomical Society © 2007 The Authors Published on behalf of Royal Astronomical Society. All rights reserved.
Date accepted:No date available
Date deposited:11 August 2014
Date of first online publication:January 2007
Date first made open access:No date available

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