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The Hard X-Ray Perspective on the Soft X-Ray Excess

Vasudevan, Ranjan V. and Mushotzky, Richard F. and Reynolds, Christopher S. and Fabian, Andrew C. and Lohfink, Anne M. and Zoghbi, Abderahmen and Gallo, Luigi C. and Walton, Dominic (2014) The Hard X-Ray Perspective on the Soft X-Ray Excess. Astrophysical Journal, 785 (1). Art. No. 30. ISSN 0004-637X. doi:10.1088/0004-637X/785/1/30.

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The X-ray spectra of many active galactic nuclei exhibit a "soft excess" below 1 keV, whose physical origin remains unclear. Diverse models have been suggested to account for it, including ionized reflection of X-rays from the inner part of the accretion disk, ionized winds/absorbers, and Comptonization. The ionized reflection model suggests a natural link between the prominence of the soft excess and the Compton reflection hump strength above 10 keV, but it has not been clear what hard X-ray signatures, if any, are expected from the other soft X-ray candidate models. Additionally, it has not been possible up until recently to obtain high-quality simultaneous measurements of both soft and hard X-ray emission necessary to distinguish these models but upcoming joint XMM-NuSTAR programs provide precisely this opportunity. In this paper, we present an extensive analysis of simulations of XMM-NuSTAR observations, using two candidate soft excess models as inputs, to determine whether such campaigns can disambiguate between them by using hard and soft X-ray observations in tandem. The simulated spectra are fit with the simplest "observer's model" of a blackbody and neutral reflection to characterize the strength of the soft and hard excesses. A plot of the strength of the hard excess against the soft excess strength provides a diagnostic plot which allows the soft excess production mechanism to be determined in individual sources and samples using current state-of-the-art and next generation hard X-ray enabled observatories. This approach can be straightforwardly extended to other candidate models for the soft excess.

Item Type:Article
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URLURL TypeDescription DOIArticle
Mushotzky, Richard F.0000-0002-7962-5446
Fabian, Andrew C.0000-0002-9378-4072
Zoghbi, Abderahmen0000-0002-0572-9613
Walton, Dominic0000-0001-5819-3552
Additional Information:© 2014 The American Astronomical Society. Received 2013 November 12; accepted 2014 February 12; published 2014 March 21. We thank the anonymous referee for useful suggestions which improved the paper. C.S.R. thanks NASA for support under grant NNX12AE13G. We thank Jeremy Sanders for help with the use of his Veusz plotting package and Cole Miller for helpful discussions on Monte-Carlo simulation techniques.
Funding AgencyGrant Number
Subject Keywords:accretion,accretion disks; galaxies COLFAML; active; X-rays COLFAML; galaxies
Issue or Number:1
Record Number:CaltechAUTHORS:20140606-081358417
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Official Citation:The Hard X-Ray Perspective on the Soft X-Ray Excess Ranjan V. Vasudevan et al. 2014 ApJ 785 30
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:46112
Deposited By: Tony Diaz
Deposited On:06 Jun 2014 17:24
Last Modified:10 Nov 2021 17:21

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