The anticorrelation between the hard X-ray photon index and the Eddington ratio in low-luminosity active galactic nuclei |
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Authors: | Minfeng Gu Xinwu Cao |
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Affiliation: | Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030, China |
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Abstract: | We find a significant anticorrelation between the hard X-ray photon index Γ and the Eddington ratio L bol/ L Edd for a sample of low-ionization nuclear emission-line regions and local Seyfert galaxies, compiled from literature with Chandra or XMM–Newton observations. This result is in contrast with the positive correlation found in luminous active galactic nuclei (AGN), while it is similar to that of X-ray binaries (XRBs) in the low/hard state. Our result is qualitatively consistent with the spectra produced from advection-dominated accretion flows (ADAFs). It implies that the X-ray emission of low-luminosity active galactic nuclei (LLAGN) may originate from the Comptonization process in ADAF, and the accretion process in LLAGN may be similar to that of XRBs in the low/hard state, which is different from that in luminous AGN. |
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Keywords: | accretion, accretion discs galaxies: active galaxies: nuclei X-rays: galaxies |
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