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A toy model for X-ray spectral variability of active galactic nuclei
High Energy Astrophysical Phenomena · Submitted 25 Jun 2014
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim We propose that such X-ray variability is caused by the change of the transition radius.
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The abstract, sentence by sentence
The long term X-ray spectral variability of ten active galactic nuclei (AGN) shows a positive spectral index-flux correlation for each object (Sobolewska & Papadakis 2009). An inner advection dominated accretion flow (ADAF) may connect to a thin disc/corona at a certain transition radius, which are responsible for hard X-ray emission in AGN. The ADAF is hot and its X-ray spectrum is hard, while the corona above the disc is relatively cold and its X-ray spectrum is therefore soft. The radiation efficiency of the ADAF is usually much lower than that of the thin disc. The increase of the transition radius may lead to decreases of the spectral index (i.e., a hard spectrum) and the X-ray luminosity even if the accretion rate is fixed, and vice versa. We propose that such X-ray variability is caused by the change of the transition radius. Our model calculations can reproduce the observed index-flux correlations, if the transition radius fluctuates around an equilibrium position, and the radiation efficiency of ADAFs is {\guillemotright} 5 per cent of that for a thin disc. The average spectral index-Eddington ratio correlation in the AGN sample can also be reproduced by our model calculations, if the equilibrium transition radius increases with decreasing mass accretion rate.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | The long term X-ray spectral variability of ten active galactic nuclei (AGN) shows a positive spectral index-flux correlation for each object (Sobolewska & Papadakis 2009). | background 0.94 | 0.07 | 0.05 | asserted 1.00 |
| s1 | An inner advection dominated accretion flow (ADAF) may connect to a thin disc/corona at a certain transition radius, which are responsible for hard X-ray emission in AGN. | method 0.54 | 0.13 | 0.04 | hedged possibility 1.00 |
| s2 | The ADAF is hot and its X-ray spectrum is hard, while the corona above the disc is relatively cold and its X-ray spectrum is therefore soft. | background 0.83 | 0.09 | 0.03 | asserted 1.00 |
| s3 | The radiation efficiency of the ADAF is usually much lower than that of the thin disc. | background 0.97 | 0.08 | 0.02 | asserted 0.95 |
| s4 | The increase of the transition radius may lead to decreases of the spectral index (i.e., a hard spectrum) and the X-ray luminosity even if the accretion rate is fixed, and vice versa. | result 0.44 | 0.45 | 0.10 | hedged possibility 0.84 |
| s5 | We propose that such X-ray variability is caused by the change of the transition radius. | contribution 0.69 | 0.64 | 0.84 | speculative 0.67 |
| s6 | Our model calculations can reproduce the observed index-flux correlations, if the transition radius fluctuates around an equilibrium position, and the radiation efficiency of ADAFs is {\guillemotright} 5 per cent of that for a thin disc. | result 0.98 | 0.93 | 0.29 | asserted 0.62 |
| s7 | The average spectral index-Eddington ratio correlation in the AGN sample can also be reproduced by our model calculations, if the equilibrium transition radius increases with decreasing mass accretion rate. | result 0.95 | 0.86 | 0.14 | asserted 0.69 |
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Original abstract
The long term X-ray spectral variability of ten active galactic nuclei (AGN) shows a positive spectral index-flux correlation for each object (Sobolewska & Papadakis 2009). An inner advection dominated accretion flow (ADAF) may connect to a thin disc/corona at a certain transition radius, which are responsible for hard X-ray emission in AGN. The ADAF is hot and its X-ray spectrum is hard, while the corona above the disc is relatively cold and its X-ray spectrum is therefore soft. The radiation efficiency of the ADAF is usually much lower than that of the thin disc. The increase of the transition radius may lead to decreases of the spectral index (i.e., a hard spectrum) and the X-ray luminosity even if the accretion rate is fixed, and vice versa. We propose that such X-ray variability is caused by the change of the transition radius. Our model calculations can reproduce the observed index-flux correlations, if the transition radius fluctuates around an equilibrium position, and the radiation efficiency of ADAFs is {\guillemotright} 5 per cent of that for a thin disc. The average spectral index-Eddington ratio correlation in the AGN sample can also be reproduced by our model calculations, if the equilibrium transition radius increases with decreasing mass accretion rate.
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2 arXiv papers cite this in 2 sentences
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It has been empirically deduced from the observations of X-ray binaries and super massive black holes in other galaxies to be [ref] , [equation] from which the end time of phase 3 is obtained to be [equation]
On the evolution of a fossil disk around neutron stars originating from merging white dwarfs · Disk Evolution · 1.00
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