Tangled magnetic field model of QPOs

ABSTRACT The highly tangled magnetic field of a magnetar supports shear waves similar to Alfvén in an ordered field. Here, we explore if torsional modes excited the stellar interior and magnetosphere can explain quasi-periodic oscillations (QPOs) observed tail giant flare SGR 1900+14. We solve initial value problem for that couples relativistic magnetosphere. Assuming arise from sudden release energy, obtain constraints on energetics geometry process. If energy is deposited initially inside star, wave propagates relatively slowly which at odds with rise time radiative event ≲ 10 ms. Nor be entirely outside as most reflects off surface, giving surface insufficient magnitude produce detectable modulations magnetospheric currents. Energy deposition volume straddles gives agreement excites range substantial amplitude QPO frequencies. In general, localized broad encompasses QPOs, though many more are than number QPOs. axisymmetrically, possible certain class MHD instabilities, considerably reduced.