On magnetic-field-induced non-geodesic corrections to relativistic orbital and epicyclic frequencies

Abstract

We discuss non-geodesic corrections to orbital and epicyclic frequencies of charged test particles orbiting a non-rotating neutron star with a dipole magnetic field. Using a fully relativistic approach we consider the influence of both the magnetic attraction and repulsion on the orbital and epicyclic motion. The magnetic repulsion introduces a rather complex and unusual behaviour of the circular orbital motion that is well defined down to the radius where the vertical epicyclic frequency loses its meaning. We demonstrate that for the intensity of the magnetic interaction appropriately restricted, the stable circular orbits extend down to the magnetic innermost stable circular orbit (MISCO) that is located well under the geodetic innermost stable circular orbit (GISCO) and even can reach the region under the photon circular orbit. The lowest stable circular orbit at rMISCOmin = 2.73M, associated with the highest possible orbital frequency , corresponds to the critical value of the particle-specific charge and the neutron star magnetic dipole moment product . For the magnetic attraction acting above the GISCO, the situation is much more simple and we demonstrate that the most significant correction arises for the radial epicyclic frequency and consequently for the location of the MISCO when the strong magnetic attraction pushes its location far behind the location of GISCO. We show that the Lorentz force also naturally violates the equality of the orbital and vertical epicyclic frequencies implied by the spherical symmetry of the background Schwarzschild geometry giving rise to the new effect of nodal precession of the orbital motion plane. Finally, we apply the magnetic attraction corrections on the relativistic precession model of the twin-peak high-frequency quasiperiodic oscillations observed in the galactic low mass x-ray binaries, showing possible high relevance of the modified radial epicyclic frequency.

Acceleration of the charged particles due to chaotic scattering in the combined black hole gravitational field and asymptotically uniform magnetic field

“…There is a large variety of studies of the charged test particle motion in such 1 Black hole immersed in an external electromagnetic field. Large-scale electromagnetic field can have dipole character for a magnetar, but at large distance from the source its character can be simplified to almost uniform magnetic field in finite element of space as shown in [7] combined fields [10,[23][24][25][26][27][28][29]. The energy from a collision of the charged particles in the vicinity of the horizon of a black hole or a naked singularity immersed into an external magnetic field can cause particle acceleration [30][31][32][33].…”

A model for 3:2 HFQPO pairs in black hole binaries based on cosmic battery

“…Thus we can fit the HFQPO pairs associated with the spectra in SPL state of each BHXB, and the BH mass and spin are in agreement with the observations. Bakala et al (2010) considered magnetic-field-induced nongeodesic corrections to charged test particles orbiting a nonrotating neutron star. It turns out that magnetic field effects are important in the fitting of HFQPOs data for some low-mass xray binaries (LMXB).…”

Appearance of innermost stable circular orbits of accretion discs around rotating neutron stars

“…viscosity, pressure forces, or magnetic field influence), and the chosen spacetime description can play some role as well (e.g. Alpar & Psaltis 2008;Straub & Šrámková 2009;Bakala et al 2010Bakala et al , 2012Kotrlová et al 2008). Despite these uncertainties, which need to be adressed in the subsequent analysis, our findings can be useful in several astrophysical applications.…”