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Article Dans Une Revue Astronomy and Astrophysics - A&A Année : 2020

Estimating the size of X-ray lamppost coronae in active galactic nuclei

F. Ursini
  • Fonction : Auteur
M. Dovciak
  • Fonction : Auteur
W. Zhang
G. Matt
  • Fonction : Auteur
C. Done
  • Fonction : Auteur

Résumé

Aims. 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.Methods. We employ a relativistic ray-tracing code, originally developed by Dovčiak and Done, that calculates the size of a Comptonizing lamppost corona illuminated by a standard thin disc. We assume that the disc extends down to the innermost stable circular orbit of a non-spinning or a maximally spinning black hole. We apply this method to a sample of 20 Seyfert 1 galaxies using simultaneous optical/UV and X-ray archival data from XMM-Newton.Results. 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.Key words: black hole physics / galaxies: active / galaxies: Seyfert / X-rays: galaxies
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Dates et versions

hal-03022642 , version 1 (24-05-2024)

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F. Ursini, M. Dovciak, W. Zhang, G. Matt, P.-O. Petrucci, et al.. Estimating the size of X-ray lamppost coronae in active galactic nuclei. Astronomy and Astrophysics - A&A, 2020, 644, pp.A132. ⟨10.1051/0004-6361/202039158⟩. ⟨hal-03022642⟩
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