**Publication date:** Aug 2015

**Abstract:**

In order to test the role of large-scale magnetic fields in quasi-

periodic oscillation phenomena observed in microquasars, we study the

oscillatory motion of charged particles in the vicinity of a

Schwarzschild black hole immersed into an external asymptotically

uniform magnetic field. We determine the fundamental frequencies of

small harmonic oscillations of charged test particles around stable

circular orbits in the equatorial plane of a magnetized black hole, and

discuss the radial profiles of frequencies of the radial and latitudinal

harmonic oscillations in dependence on the mass of the black hole and

the strength of the magnetic field. We demonstrate that assuming

relevance of resonant phenomena of the radial and latitudinal

oscillations of charged particles at their frequency ratio 3 :2, the

oscillatory frequencies of charged particles can be well related to the

frequencies of the twin high-frequency quasi-periodic oscillations

observed in the microquasars GRS 1915+105, XTE 1550-564 and GRO 1655-40.

**Authors:**

Kološ, Martin; Stuchlík, Zdeněk; Tursunov, Arman;