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Simulated spectral states of AGN and observational predictions

Active galactic nuclei (AGN) and galactic black hole binaries (GBHs) represent two classes of accreting black holes. They both contain an accretion disc emitting a thermal radiation, and a non-thermal X-ray emitting corona. GBHs exhibit state transitions, and their spectral states are characterized by different luminosity levels and shapes of the spectral energy distribution (SED). If AGN transitioned in a similar way, the characteristic timescales of such transitions would exceed ~10^5 years. Thus, the probability to observe an individual AGN transiting between different spectral states is very low. In this paper we follow a spectral evolution of a GBH, GRO~J1655-40, and then apply its SED evolution pattern to a simulated population of AGN under an assumption that a large sample of AGN should contain a mixture of sources in different spectral states. We model the X-ray spectra of GRO J1655-40 with the eqpair model and then scale the best-fitting models with the black hole mass to simulate the AGN spectra. We compare the simulated and observed AGN SEDs to determine the spectral states of observed Type 1 AGN, LINER and NLS1 populations. We conclude that bright Type 1 AGN and NLS1 galaxies are in a spectral state similar to the soft spectral state of GBHs, while the spectral state of LINERs may correspond to the hard spectral state of GBHs. We find that taking into account a spread in the black hole masses over several orders of magnitude, as in the observed AGN samples, leads to a correlation between the X-ray loudness and the monochromatic luminosity at 2500A, similar to that found in observations. We predict however that the correlation changes its sign around a critical luminosity of L_crit ~ 0.01 L_E.