The role of absorption and reflection in the soft X-ray excess of Active Galactic Nuclei

Chevallier, L.; Collin, S.; Dumont, A. M.; Czerny, B.; Mouchet, M.; Gonçalves, A. C.; Goosmann, R. W.

doi:10.1051/0004-6361:20053730

Cited by 50 publications

(106 citation statements)

References 56 publications

Supporting

Mentioning

105

Contrasting

Order By: Relevance

“…Temperature decreases at larger depths into the cloud where scattering reduces the heating, so the density must increase to keep in pressure balance. This lower ionization state material has more line cooling, so the temperature drops abruptly, giving a sharp transition between a highly ionized skin and a nearly neutral core (Chevallier et al 2006). Reflection from such structures, especially with a turbulent velocity field, may be a feasible way to reproduce the observed 2-10 keV spectra in the dips.…”

Section: Discussionmentioning

confidence: 99%

Complex narrow-line Seyfert 1s: high spin or high inclination?

Gardner

Done

2015

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

Complex narrow line Seyfert 1s (NLS1s), such as 1H0707-495, differ from simple NLS1s like PG1244+026 by showing stronger broad spectral features at Fe K and larger amplitude flux variability. These are correlated: the strongest Fe K features are seen during deep dips in the light curves of complex NLS1s. There are two competing explanations for these features, one where a compact X-ray source on the spin axis of a highly spinning black hole approaches the horizon and the consequent strong relativistic effects focus the intrinsic flux onto the inner edge of a thin disc, giving a dim, reflection dominated spectrum. The other is that the deep dips are caused by complex absorption by clumps close to the hard X-ray source. The reflection dominated model is able to reproduce the very short 30s soft lag from reverberation seen in the complex NLS1 1H0707-495. However, it does not explain the characteristic switch to hard lags on longer timescales. Instead, a full model of propagating fluctuations coupled to reverberation can explain the switch in the simple NLS1 PG1244+026 using a low spin black hole. However PG1244+026 has a longer reverberation lag of ∼ 200s.Here we extend the successful propagation-reverberation model for the simple NLS1 PG1244+026 to include the effect of absorption from clumps in a turbulent region above the disk. The resulting occultations of the inner accretion flow can introduce additional hard lags when relativistic effects are taken into account. This dilutes the soft lag from reverberation and shifts it to higher frequencies, making a smooth transition between the 200s lags seen in simple NLS1s to the 30s lags in complex NLS1s. These two classes of NLS1 could then be determined by inclination angle with respect to a clumpy, probably turbulent, failed wind structure on the disc.

show abstract

Section: Discussionmentioning

confidence: 99%

Complex narrow-line Seyfert 1s: high spin or high inclination?

Gardner

Done

2015

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

show abstract

“…The PCF model assumes that some fraction, f , of the X-ray source is covered by a neutral absorber with a column density of N H,z , while the rest is unobscured. This could be responsible for an apparent soft excess in two different geometries, either by reflection from optically thick material out of the line of sight , or absorption by optically thin material along the line of sight (Gierliński & Done 2004;Chevallier et al 2006). On the other hand, there are some possible ways of explaining the soft excess from the disc itself in terms of the reprocessing of the primary X-rays in the accretion disc as reflected emission from a geometrically flat disc, with solar abundances, illuminated by an isotropic source.…”

Section: Missing-agn Subsamplementioning

confidence: 99%

The X-ray luminous galaxies optically classified as star forming are mostly narrow line Seyfert 1 s

Castelló-Mor

Barcons

Ballo

et al. 2012

A&A

View full text Add to dashboard Cite

Context. The optical and ultraviolet emission lines of galaxies are widely used to distinguish star-forming (SF) galaxies from active galactic nuclei (AGNs). However, this type of diagnostic has some associated uncertainties, because AGNs can be of low luminosity and/or heavily obscured, and the optical emission lines may be dominated by a stellar component. On the other hand, and despite its limitations, X-ray emission can be used as a reliable tracer of luminous AGNs. Several well-studied examples exist where the optical diagnostics are indicative of SF galaxy, but the X-ray properties reveal the presence of an AGN. Aims. We aim to characterize the nature of galaxies whose optical emission line diagnostics are consistent with star formation, but whose X-ray properties strongly point towards the presence of an AGN. Understanding these sources is of particular importance in assessing the completeness of AGN samples derived from large galaxy surveys, selected solely on the basis of their optical spectral properties. Methods. We construct a large sample of 211 narrow emission line galaxies (NELGs, which have full widths at half maximum (FWHMs) H β emission line <1200 km s −1 ) from the SDSS-DR7 galaxy spectroscopic catalogue, for which we are able to construct a classical diagnostic diagram, [OIII]/H β versus [NII]/H α (hence z < 0.4), and that are also detected in the 2−10 keV X-ray band and present in the 2XMM X-ray source catalogue. This sample offers a large database by which to investigate potential mismatches between optical diagnostics and X-ray emission. Results. Among these 211 objects, which based on our selection criteria all are all at z < 0.4, we find that 145 galaxies are diagnosed as AGNs, having 2−10 keV X-ray luminosities that span a wide range, from 10 40 erg/s to above 10 44 erg/s. Out of the remaining 66 galaxies, which are instead diagnosed as "star-forming", we find a bimodal distribution in which 28 have X-ray luminosities in excess of 10 42 erg/s, large thickness parameters (T = F 2−10 keV /F [OIII] > 1) and large X-ray to optical flux ratios (X/O > 0.1), while the rest are consistent with being simply starforming galaxies. Those 28 galaxies exhibit the broadest H β line widths (FWHMs from ∼300 to 1200 km s −1 ), and their X-ray spectrum is steeper than average and often displays a soft excess. Conclusions. We therefore conclude that the population of X-ray luminous NELGs with optical lines consistent with those of a starforming galaxy (which represent 19% of our whole sample) is largely dominated by narrow line Seyfert 1s (NLS1s). The occurrence of such sources in the overall optically selected sample is small (<2%), hence the contamination of optically selected galaxies by NLS1s is very small.

show abstract

“…Finally, the inner-disc temperature in the CD model is in the same range as the characteristic temperature of the soft excess in Seyfert 1s, despite the large mass difference between ULXs and Active Galactic Nuclei (AGN). Both kinds of spectra can formally be well fitted with a cool disc-blackbody component plus a powerlaw, but more likely the soft excess in AGN could be explained by a combination of blurred emission/absorption lines and reflection (Gierliński & Done 2004;Chevallier et al 2006); this could suggest that ULXs and stellar-mass BHs are completely separate classes of sources. Instead, characteristic disc temperatures in the HD model fall within, or close to, the range of stellar-mass BH temperature; this could suggest that ULXs are simply an extension of the stellar-mass class at higher accretion rates.…”

Section: Hot-disc Vs Cold-disc Modelsmentioning

confidence: 99%

Soft‐excess in ULX spectra: disc emission or wind absorption?

Gonçalves

Soria

2007

AIP Conference Proceedings

Self Cite

View full text Add to dashboard Cite

Abstract. We assess the claim that Ultra-luminous X-ray sources (ULXs) host intermediate-mass black holes (BH) by comparing the cool disc-blackbody model with a range of other models, namelly a more complex physical model based on a power-law component slightly modified at various energies by smeared emission/absorption lines from highly-ionized gas. Our main conclusion is that the presence of a soft excess, or a soft deficit, depends entirely on the energy range to which we choose to fit the "true" power-law continuum; hence, we argue that those components should not be taken as evidence for accretion disc emission, nor used to infer BH masses. We speculate that bright ULXs could be in a spectral state similar to (or an extension of) the steep-power-law state of Galactic BH candidates, in which the disc is completely comptonized and not directly detectable, and the power-law emission may be modified by the surrounding, fast-moving, ionized gas.

show abstract

The role of absorption and reflection in the soft X-ray excess of Active Galactic Nuclei

Cited by 50 publications

References 56 publications

Complex narrow-line Seyfert 1s: high spin or high inclination?

Complex narrow-line Seyfert 1s: high spin or high inclination?

The X-ray luminous galaxies optically classified as star forming are mostly narrow line Seyfert 1 s

Soft‐excess in ULX spectra: disc emission or wind absorption?

Contact Info

Product

Resources

About