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Estimating the size of X-ray lamppost coronae in active galactic nuclei
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SYSNO ASEP 0538501 Document Type J - Journal Article R&D Document Type Journal Article Subsidiary J Článek ve WOS Title Estimating the size of X-ray lamppost coronae in active galactic nuclei Author(s) Ursini, F. (IT)
Dovčiak, Michal (ASU-R) RID, ORCID
Zhang, Wenda (ASU-R) ORCID
Matt, G. (IT)
Petrucci, P. O. (FR)
Done, C. (GB)Article number A132 Source Title Astronomy & Astrophysics. - : EDP Sciences - ISSN 0004-6361
Roč. 644, December (2020)Number of pages 9 s. Publication form Online - E Language eng - English Country FR - France Keywords black hole physics ; active galaxies ; X-rays Subject RIV BN - Astronomy, Celestial Mechanics, Astrophysics OECD category Astronomy (including astrophysics,space science) R&D Projects GA17-02430S GA ČR - Czech Science Foundation (CSF) Method of publishing Limited access Institutional support ASU-R - RVO:67985815 UT WOS 000599907300002 EID SCOPUS 85097865420 DOI 10.1051/0004-6361/202039158 Annotation We report estimates of the X-ray coronal size of active galactic nuclei in the lamppost geometry. In this commonly adopted scenario, the corona is assumed for simplicity to be a point-like X-ray source located on the axis of the accretion disc. However, the corona must intercept a number of optical/UV seed photons from the disc consistent with the observed X-ray flux, which constrains its size. At least for the sources accreting below the Eddington limit, we find that a Comptonizing lamppost corona can generally exist, but with constraints on its size and height above the event horizon of the black hole depending on the spin. For a maximally spinning black hole, a solution can almost always be found at any height, while for a non-spinning black hole the height must generally be higher than 5 gravitational radii. This is because, for a given luminosity, a higher spin implies more seed photons illuminating the corona, which is due to a larger and hotter inner disc area. The maximal spin solution is favoured, as it predicts an X-ray photon index in better agreement with the observations. Workplace Astronomical Institute Contact Radka Svašková, bibl@asu.cas.cz, Tel.: 323 620 326 Year of Publishing 2021 Electronic address https://doi.org/10.1051/0004-6361/202039158
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