2009/02/11 by A. Colaiuda, H. Beyer, K. D. Kokkotas · 1 citation
Physics and Astronomy · #Astrophysical Phenomena and Observations #Constant (computer programming) #Dipole #Magnetar #Magnetic dipole #Magnetic energy #Magnetic field #Neutron star #Pulsars and Gravitational Waves Research #Scientific Research and Discoveries #Toroid #astro-ph.HE #astro-ph.SR #gr-qc
paper · pdf · doi:10.1111/j.1365-2966.2009.14878.x
published as Mon.Not.Roy.Astron.Soc.396:1441,2009 · 8 pages, 7 figures
arxiv created 2009/02/11 · openalex publication_date 2009/06/02 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We study torsional Alfv'en oscillations of magnetars, i.e., neutron stars with a strong magnetic field. We consider the poloidal and toroidal components of the magnetic field and a wide range of equilibrium stellar models. We use a new coordinate system (X,Y), where X=√(a1) sin θ, Y=√(a1)cos θ and a1 is the radial component of the magnetic field. In this coordinate system, the 1+2-dimensional evolution equation describing the quasi-periodic oscillations, QPOs, see Sotani et al. (2007), is reduced to a 1+1-dimensional equation, where the perturbations propagate only along the Y-axis. We solve the 1+1-dimensional equation for different boundary conditions and open magnetic field lines, i.e., magnetic field lines that reach the surface and there match up with the exterior dipole magnetic field, as well as closed magnetic lines, i.e., magnetic lines that never reach the stellar surface. For the open field lines, we find two families of QPOs frequencies; a family of "lower" QPOs frequencies which is located near the X-axis and a family of "upper" frequencies located near the Y-axis. According to Levin (2007), the fundamental frequencies of these two families can be interpreted as the turning points of a continuous spectrum. We find that the upper frequencies are constant multiples of the lower frequencies with a constant equaling 2n+1. For the closed lines, the corresponding factor is n+1 . By these relations, we can explain both the lower and the higher observed frequencies in SGR 1806-20 and SGR 1900+14.