Torsional Oscillations of Relativistic Stars with Dipole Magnetic Fields II. Global Alfvén Modes

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dc.creatorSotani, H.
dc.creatorKokkotas, K. D.
dc.creatorStergioulas, N.
dc.creatorVavoulidis, M.
dc.date2006-11-21
dc.date.accessioned2026-07-07T07:30:54Z
dc.date.available2026-07-07T07:30:54Z
dc.descriptionWe investigate torsional Alfvén modes of relativistic stars with a global dipole magnetic field. It has been noted recently (Glampedakis et al. 2006) that such oscillation modes could serve as as an alternative explanation (in contrast to torsional crustal modes) for the SGR phenomenon, if the magnetic field is not confined to the crust. We compute global Alfvén modes for a representative sample of equations of state and magnetar masses, in the ideal MHD approximation and ignoring $\ell \pm 2$ terms in the eigenfunction. We find that the presence of a realistic crust has a negligible effect on Alfvén modes for $B > 4\times 10^{15}$ G. Furthermore, we find strong avoided crossings between torsional Alfvén modes and torsional crust modes. For magnetar-like magnetic field strengths, the spacing between consecutive Alfvén modes is of the same order as the gap of avoided crossings. As a result, it is not possible to identify modes of predominantly crustal character and all oscillations are predominantly Alfvén-like. Interestingly, we find excellent agreement between our computed frequencies and observed frequencies in two SGRs, for a maximum magnetic field strenght in the range of (0.8--1.2)$\times 10^{16}$ G.
dc.description13 pages, 8 figures
dc.identifierhttps://arxiv.org/abs/astro-ph/0611666
dc.identifierhttp://arxiv.org/abs/astro-ph/0611666
dc.identifier.urihttp://salesiana.dossiersoluciones.com/handle/123456789/118564
dc.subjectAstrophysics
dc.subjectGeneral Relativity and Quantum Cosmology
dc.titleTorsional Oscillations of Relativistic Stars with Dipole Magnetic Fields II. Global Alfvén Modes
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