A1 Refereed original research article in a scientific journal
Doughnut strikes sandwich: the geometry of hot medium in accreting black hole X-ray binaries
Authors: Juri Poutanen, Alexandra Veledina, Andrzej A. Zdziarski
Publisher: EDP SCIENCES S A
Publication year: 2018
Journal: Astronomy and Astrophysics
Journal name in source: ASTRONOMY & ASTROPHYSICS
Journal acronym: ASTRON ASTROPHYS
Article number: ARTN A79
Volume: 614
Number of pages: 12
ISSN: 1432-0746
DOI: https://doi.org/10.1051/0004-6361/201732345
Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/32808492
We study the effects of the mutual interaction of hot plasma and cold medium in black hole binaries in their hard spectral state. We consider a number of different geometries. In contrast to previous theoretical studies, we use a modern energy-conserving code for reflection and reprocessing from cold media. We show that a static corona above an accretion disc extending to the innermost stable circular orbit produces spectra not compatible with those observed. They are either too soft or require a much higher disc ionization than that observed. This conclusion confirms a number of previous findings, but disproves a recent study claiming an agreement of that model with observations. We show that the cold disc has to be truncated in order to agree with the observed spectral hardness. However, a cold disc truncated at a large radius and replaced by a hot flow produces spectra which are too hard if the only source of seed photons for Comptonization is the accretion disc. Our favourable geometry is a truncated disc coexisting with a hot plasma either overlapping with the disc or containing some cold matter within it, also including seed photons arising from cyclo-synchrotron emission of hybrid electrons, i.e. containing both thermal and non-thermal parts.
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