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

Abstract

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 αGBH 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, αOX, used to describe AGN spectra. We do not find linear correlation between the αGBH and disc flux (similar to that between αOX and optical/UV luminosity found in AGN). Instead, we show that αGBH follows a well-defined pattern during a GBH outburst. We find that αGBH 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 (αGBH 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 αOX and Γ with the optical/UV and X-ray 2 keV fluxes considered for AGN and quasars. © 2009 RAS.