Excitation of low-frequency QPOs in black-hole accretion

Details Excitation of low-frequency QPOs in black-hole accretion Excitation of low-frequency QPOs in black-hole accretion

2004-07-22

arxiv.org/abs/astro-ph/0407474v1

Astron.Astrophys. 427 (2004) 251-261

Astronomy and Astrophysics

Astrophysics

11 pages, 5 figures, accepted for publication in A&A

Scientific paper

10.1051/0004-6361:200400043

We study possible mechanisms of excitation of quasiperiodic oscillations in the accretion flow of black hole accreters in their hard spectral states, in the context of the `truncated disk' model. Quasi-spherical oscillations of the inner ion-supported accretion flow (ISAF) can be excited by the interaction of this hot flow with the cool disk extending outward from it. The fundamental mode of (p-mode) oscillation is most easily excited, and has a frequency near the Kepler frequency at the inner edge of the cool disk. The strongest excitation mechanism is a feedback loop involving cooling of the ISAF by soft photons from the cool disk and heating of the cool disk by the ISAF, while synchrotron emission can be a relatively strong damping effect. Growth times are computed by detailed Comptonization calculations of the interaction of an idealized ISAF with a cool disk. Typical growth times as short as a few dynamical times are found, while amplitudes can be as large as 10%.

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