What can we learn about quasars from alpha_OX measurements in galactic black hole binaries?

TL;DR

This study compares spectral energy distributions of AGN and Galactic black hole binaries using a unified parameter, revealing that most AGN are in a spectral state similar to the very high/intermediate state of GBHs.

Contribution

It introduces a new spectral parameter, alpha_GBH, for GBHs, and demonstrates its similarity to alpha_OX in AGN, providing insights into their spectral states and accretion processes.

Findings

Alpha_GBH clusters around 1, 1.5, and 2, corresponding to different spectral states.

Most AGN are in a spectral state akin to the very high/intermediate state of GBHs.

Alpha_GBH varies with disc and Comptonization fluxes, reflecting spectral state changes.

Abstract

We draw a comparison between AGN and Galactic black hole binaries using a uniform description of spectral energy distribution of these two classes of accreting X-ray sources. We parametrize spectra of GBHs with an alpha_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, alpha_OX, used to describe AGN spectra. We do not find linear correlation between the alpha_GBH and disc flux (similar to that between alpha_OX and optical/UV luminosity found in AGN). Instead, we show that alpha_GBH follows a well defined pattern during a GBH outburst. We find that alpha_GBH tend to cluster around 1, 1.5 and 2, which correspond to a hard, very high/intermediate and soft spectral state, respectively. We conclude that majority of the observed Type 1 radio quiet AGN are in a spectral state corresponding to a very high/intermediate state of GBHs. The same conclusion is valid for radio loud AGN. We also study variations of the spectral slopes (alpha_GBH and the X-ray photon index, Gamma) as a function of disc and Comptonization fluxes. We discuss these dependencies in the context of correlations of alpha_OX and Gamma with the optical/UV and X-ray 2 keV fluxes considered for AGN and quasars.