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We find a significant anticorrelation between the hard X-ray photon index Gamma 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.
Gu et al. (2009) studied this question.