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Astron. Astrophys. 362, L41-L44 (2000)

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Letter to the Editor

Truncated disks - advective tori solutions around BHs

I. The effects of conduction and enhanced Coulomb coupling

A. Hujeirat and M. Camenzind

Landessternwarte Königstuhl, Königsstuhl 12, 69117 Heidelberg, Germany

Received 28 September 2000 / Accepted 10 October 2000


We present the first 2D quasi-stationary radiative hydrodynamical calculations of accretion flows onto BHs taking into account cooling via Bremsstrahlung, Compton, Synchrotron and conduction. The effect of enhanced Coulomb coupling is investigated also.

Based on the numerical results obtained, we find that two-temperature (2T) accretion flows are best suited to describe hard states, and one-temperature (1T) in the soft states, with transition possibly depending on the accretion rate. In the 2T case, the ion-conduction enlarges the disk-truncation-radius from 5 to 9 Schwarzschild radii ([FORMULA]). The ion-pressure powers outflows, hence substantially decreasing the accretion rate with decreasing radius. The spectrum is partially modified BB with hard photons emitted from the inner region and showing a cutoff at [FORMULA].

In the 1T case, conduction decreases the truncation radius from 7 to [FORMULA] and lowers the maximum gas temperature. The outflows are weaker, the spectrum is pre-dominantly modified BB and the emitted photons from the inner region are much harder (up to [FORMULA]). In both cases, the unsaturated Comptonization region coincides with the transition region between the disk and the advective torus.

When gradually enhancing the Coulomb coupling, we find that the ion-temperature [FORMULA] decreases and the electron temperature [FORMULA] increases, asymptotically converging to 1T flows. However, once the dissipated energy goes into heating the ions, ion-electron thermal decoupling is inevitable within the last stable orbit ([FORMULA]) even when the Coulomb interaction is enhanced by an additional two orders of magnitude.

Key words: magnetic fields – Magnetohydrodynamics (MHD) – accretion, accretion disks – black hole physics – hydrodynamics – methods: numerical

Send offprint requests to: A. Hujeirat

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© European Southern Observatory (ESO) 2000

Online publication: October 30, 2000