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Evolution of bimodal accretion flows

J. Gracia·J. Peitz·Ch. Keller·M. Camenzind
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Abstract

We consider time-dependent models for rotating accretion flows onto black holes, where a transition takes place from an outer cooling-dominated disc to a radiatively inefficient flow in the inner region. In order to allow for a transition of this type we solve the energy equation, both, for the gas and for the radiation field, including a radiative cooling flux and a turbulent convective heat flux directed along the negative entropy gradient. The transition region is found to be highly variable, and a corresponding variation expected for the associated total luminosity. In particular, rapid oscillations of the transition radius are present on a timescale comparable with the local Keplerian rotation time. These oscillations are accompanied by a quasi-periodic modulation of the mass flux at the outer edge of the advection-dominated accretion flow (ADAF). We speculate about the relevance for the high-frequency QPO phenomenon.

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J. Gracia, J. Peitz, Ch. Keller, M. Camenzind. 2003-05-26. Evolution of bimodal accretion flows. https://doi.org/10.1046/j.1365-8711.2003.06832.x

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