Journal Article

What can we learn about quasars from α<sub>OX</sub> measurements in Galactic black hole binaries?

Małgorzata A. Sobolewska, Marek Gierliński and Aneta Siemiginowska

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 394, issue 3, pages 1640-1648
Published in print April 2009 | ISSN: 0035-8711
Published online April 2009 | e-ISSN: 1365-2966 | DOI:
What can we learn about quasars from αOX measurements in Galactic black hole binaries?

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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.

Keywords: accretion, accretion discs; galaxies: active; quasars: general; X-ray: binaries; X-rays: galaxies

Journal Article.  6565 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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