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X-ray emission from hot accretion flows

Published online by Cambridge University Press:  25 July 2014

Andrzej Niedźwiecki
Affiliation:
Department of Astrophysics, University of Łódź, Pomorska 149/153, 90-236 Łódź, Poland email: niedzwiecki@uni.lodz.pl
Fu-Guo Xie
Affiliation:
Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030, China email: fgxie@shao.ac.cn
Agnieszka Stȩpnik
Affiliation:
Department of Astrophysics, University of Łódź, Pomorska 149/153, 90-236 Łódź, Poland email: niedzwiecki@uni.lodz.pl
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Abstract

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Radiatively inefficient, hot accretion flows are widely considered as a relevant accretion mode in low-luminosity AGNs. We study spectral formation in such flows using a refined model with a fully general relativistic description of both the radiative (leptonic and hadronic) and hydrodynamic processes, as well as with an exact treatment of global Comptonization. We find that the X-ray spectral index–Eddington ratio anticorrelation as well as the cut-off energy measured in the best-studied objects favor accretion flows with rather strong magnetic field and with a weak direct heating of electrons. Furthermore, they require a much stronger source of seed photons than considered in previous studies. The nonthermal synchrotron radiation of relativistic electrons seems to be the most likely process capable of providing a sufficient flux of seed photons. Hadronic processes, which should occur due to basic properties of hot flows, provide an attractive explanation for the origin of such electrons.

Type
Contributed Papers
Copyright
Copyright © International Astronomical Union 2014 

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