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;