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

Małgorzata A. Sobolewska (Lead / Corresponding author), Marek Gierliński, Aneta Siemiginowska

    Research output: Contribution to journalArticlepeer-review

    24 Citations (Scopus)


    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.

    Original languageEnglish
    Pages (from-to)1640-1648
    Number of pages9
    JournalMonthly Notices of the Royal Astronomical Society
    Issue number3
    Early online date3 Apr 2009
    Publication statusPublished - 11 Apr 2009


    • Accretion, accretion discs
    • Galaxies: active
    • Quasars: general
    • X-ray: binaries
    • X-rays: galaxies

    ASJC Scopus subject areas

    • Astronomy and Astrophysics
    • Space and Planetary Science


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