An Explanation for the soft X-ray excess in AGN

By J. Crummy, A. C. Fabian, L. Gallo, R. Ross. 2005

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We present a large sample of type 1 active galactic nuclei (AGN) spectra taken with XMM-Newton, and fit them with both the conventional model (a power law and black body) and the relativistically-blurred photoionized disc reflection model of Ross & Fabian (2005). We find the disc reflection model is a better fit. The disc reflection model successfully reproduces the continuum shape, including the soft excess, of all the sources. The model also reproduces many features that would conventionally be interpreted as absorption edges. We are able to use the model to infer the properties of the sources, specifically that the majority of black holes in the sample are strongly rotating, and that there is a deficit in sources with an inclination > 70 ◦ . We conclude that the disc reflection model is an important tool in the study of AGN X-ray spectra.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/1924b71d06484d1c63aee0583f265ccfd37990cf

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Citations in the corpus

Suzaku observations of 'bare' active galactic nuclei (2012, background): “These effects can blend the soft complex of reflected emission lines together into a smooth emission feature, offering a natural explanation for the soft excess frequently observed in the spectra of AGN (Crummy et al. 2006).”
The Suzaku View of Highly Ionized Outflows in AGN. 1; Statistical Detection and Global Absorber Properties (2012, background): “…either the transmitted or reflected flux along the sight line through smeared absorption (e.g. Chevallier et al. 2006; Done & Nayakshin 2007; Sobolewska & Done 2007) or blurred reflection (e.g. Crummy et al. 2006; Brenneman et al. 2011; Nardini et al. 2011; Nardini, Fabian & Walton 2012) effects.”
Intrinsic disc emission and the soft X‐ray excess in active galactic nuclei (2011, background): “…can be smeared by strong relativistic effects in the reflection model, but the parametersr quired are quite extreme (the disc has to extend down to the last stable orbit of a high spin black hole, with reflection emissivity which ishighly concentrated to the innermost regions: Crummy et al. 2006).”
A Combined Optical and X-ray Study of Unobscured Type 1 AGN. I. Optical Spectra and SED Modeling (2011, methodology): “The origin of this so-called soft X-ray excess is still unclear (e.g. Gierliński & Done 2004; Crummy et al. 2006; Turner et al. 2007; Miller, Turner & Reeves 2008), and so some previous broadband SED modelling studies have explicitly excluded data below 1 keV.”
Broad iron L line and X-ray reverberation in 1H0707-495 (2009, background): “It appears to be well explained by the blend of relativistically smeared reflection continuum (Crummy et al. 2006; see Schurch & Done 2008 for problems with alternative absorption models).”
XMM–Newton observations of the brightest ultraluminous X-ray sources (2006, background): “…note that one interesting suggestion, that has recently been found to work in some AGN X-ray spectra, is that the soft excess could arise in relativistically-blurred atomic fea- c© 2004 RAS, MNRAS000, 1–16 tures found in the reflection spectrum of a photoionised accretion disc (Crummy et al. 2006).”
An XMM–Newton survey of broad iron lines in Seyfert galaxies (2007, methodology): “We account for this using a blurring model (Fabian et al. 2002; Crummy et al. 2006) which convolves a given spectrum with the kernel from the relativistic accretion disk line model of Laor (1991).”
Relativistic iron K X-ray reverberation in NGC 4151 (2011, background): “Although this interpretation fails when a complete set of observables (variability power, flux and lag spectra) are considered (Zoghbi et al. 2011), it stands on the ambiguity in interpreting the soft excess itself (e.g. Crummy et al. 2006; Done et al. 2011).”
The synthesis of the cosmic X-ray background in the Chandra and XMM-Newton era (2006, background): “…objects, which has been interpreted either as the exponn- tial tail of the thermal emission from the accretion disk (Czerny & Elvis 1987) or more recently as due to a mildly ionized re- flection component including a blend of emission lines blurred by relativistic effects (Crummy et al. 2006).”
CAIXA: a catalogue of AGN in the XMM-Newton archive - II. Multiwavelength correlations (2009, background): “…interpretation of the soft excess as direct emission from the accretion disc was questioned when several studies (e.g. Gierliński & Done 2004; Crummy et al. 2006) showed that the observed temperature of the resulting black body is remarkably constant across orders of magnitude of…”
A physical model of the broad-band continuum of AGN and its implications for the UV/X relation and optical variability (2018, background): “Alternatively, it could be produced by reprocessing/reflection of the coronal emission on the very inner disc, where extremely © 2018 The Authors strong relativistic effects smear out the expected strong line emission from ionised material (Crummy et al. 2006).”