MHD simulations of oscillating cusp-filling tori around neutron stars -- missing upper kHz QPO

Abstract

We performed axisymmetric, grid-based, ideal magnetohydrodynamic (MHD) simulations of oscillating cusp-filling tori orbiting a non-rotating neutron star. A pseudo-Newtonian potential was used to construct the constant angular momentum tori in equilibrium. The inner edge of the torus is terminated by a "cusp" in the effective potential. The initial motion of the model tori was perturbed with uniform sub-sonic vertical and diagonal velocity fields. As the configuration evolved in time, we measured the mass accretion rate on the neutron star surface and obtained the power spectrum. The prominent mode of oscillation in the cusp torus is the radial epicyclic mode. It would appear that vertical oscillations are suppressed by the presence of the cusp. From our analysis it follows that the mass accretion rate carries a modulation imprint of the oscillating torus, and hence so does the boundary layer luminosity.

arXiv commentAccepted in MNRAS Letters. 5 pages, 3 figures, 1 table

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Cited by in corpus (4)

• Timescale of twin-peak quasi-periodic oscillations and mass of accreting neutron stars
• Epicyclic oscillations in the Hartle-Thorne external geometry
• Simple analytic formula relating the mass and spin of accreting compact objects to their rapid X-ray variability
• A possible explanation of the parallel tracks in kilohertz quasi-periodic oscillations from low-mass-X-ray binaries