**Publication date:** Dec 2007

**Abstract:**

Several models of the X-ray flux modulation observed in the low-mass X-ray binaries (LMXBs), in particular the neutron star LMXBs, deal with Keplerian and epicyclic frequencies of geodesic orbital motion. We discuss non-geodesic corrections to the orbital and epicyclic frequencies of charged test particles caused by presence of a neutron star magnetic field. The magnetic field is considered to be generated by an intrinsic static dipole magnetic moment of a neutron star represented by the Schwarzschild geometry. We present fully general relativistic formulae for the orbital and epicyclic frequencies, obtained using the appropriate equations governing perturbations of the circular motion. The most significant correction arises for the radial epicyclic frequency. The zero point of the corrected radial epicyclic frequency defines radius of the effective innermost stable circular orbit „(EISCO).“ The dipole magnetic field also violates equality of the orbital and vertical epicyclic frequencies corresponding to the spherical symmetry of the Schwarzschild geometry.

**Authors:**

Bakala, Pavel; Šrámková, Eva; Stuchlík, Zdeněk; Török, Gabriel;