Astronomy and Astrophysics – Astrophysics – High Energy Astrophysical Phenomena
Scientific paper
2010-06-18
2011, MNRAS, 410, 399
Astronomy and Astrophysics
Astrophysics
High Energy Astrophysical Phenomena
21 pages, 11 figures, MNRAS accepted
Scientific paper
10.1111/j.1365-2966.2010.17451.x
Low-order, non-axisymmetric p-modes (also referred as inertial-acoustic modes) trapped in the inner-most region of hydrodynamic accretion discs around black holes, are plausible candidates for high-frequency quasi-periodic oscillations (QPOs) observed in a number of accreting black-hole systems. These modes are subject to global instabilities due to wave absorption at the corotation resonance (where the wave pattern frequency $\omega/m$ equals the disc rotation rate $\Omega$), when the fluid vortensity, $\zeta=\kappa^2/(2\Omega\Sigma)$ (where $\kappa$ and $\Sigma$ are the radial epicyclic frequency and disc surface density, respectively), has a positive gradient. We investigate the effects of disc magnetic fields on the wave absorption at corotation and the related wave super-reflection of the corotation barrier, and on the overstability of disc p-modes. For discs with a pure toroidal field, the corotation resonance is split into two magnetic resonances, where the wave frequency in the corotating frame of the fluid, $\tomega=\omega-m\Omega$, matches the slow magnetosonic wave frequency. Significant wave energy/angular momentum absorption occurs at both magnetic resonances, but with opposite signs. The combined effect of the two magnetic resonances is to reduce the super-reflection and the growth rate of the overstable p-modes. We show that even a subthermal toroidal field may suppress the overstability of hydrodynamic (B=0) p-modes. For accretion discs with mixed (toroidal and vertical) magnetic fields, two additional Alfven resonances appear, where $\tomega$ matches the local Alfven wave frequency. They further reduce the growth rate of p-modes. Our results suggest that in order for the non-axisymmetric p-modes to be a viable candidate for the observed high-frequency QPOs, the disc magnetic field must be appreciably subthermal, or other mode excitation mechanisms are at work.
Fu Wen
Lai Dong
No associations
LandOfFree
Corotational Instability, Magnetic Resonances and Global Inertial-Acoustic Oscillations in Magnetized Black-Hole Accretion Discs does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Corotational Instability, Magnetic Resonances and Global Inertial-Acoustic Oscillations in Magnetized Black-Hole Accretion Discs, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Corotational Instability, Magnetic Resonances and Global Inertial-Acoustic Oscillations in Magnetized Black-Hole Accretion Discs will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-261247