What can we learn about quasars from αOX measurements in Galactic black hole binaries?

We draw a comparison between active galactic nuclei (AGN) and Galactic black hole binaries (GBHs) using a uniform description of spectral energy distribution of these two classes of X-ray sources. We parametrize spectra of GBHs with an α _GBH parameter which we define as a slope of a nominal power-law function between 3 and 20 keV. We show that this parameter can be treated as an equivalent of the X-ray loudness, α _OX, used to describe AGN spectra. We do not find linear correlation between the α _GBH and disc flux (similar to that between α _OX and optical/UV luminosity found in AGN). Instead, we show that α _GBH follows a well-defined pattern during a GBH outburst. We find that α _GBH tend to cluster around 1, 1.5 and 2, which corresponds to the hard, very high/intermediate and soft spectral states, respectively. We conclude that majority of the observed Type 1 radio quiet AGN are in the spectral state corresponding to the very high/intermediate state of GBHs. The same conclusion is valid for radio-loud AGN. We also study variations of the spectral slopes (α _GBH and the X-ray photon index, Γ) as a function of disc and Comptonization fluxes. We discuss these dependencies in the light of correlations of α _OX and Γ with the optical/UV and X-ray 2 keV fluxes considered for AGN and quasars.