A Magnetic Flux Tube Oscillation Model for QPOs in SGR Giant Flares

Giant flares from soft gamma-ray repeaters (SGRs) are one of the most violent phenomena in neutron stars. Quasi-periodic oscillations (QPOs) with frequencies ranging from 18 to 1840 Hz have been discovered in the tails of giant flares from two SGRs, and were ascribed to be seismic vibrations or torsional oscillations of magnetars. Here we propose an alternative explanation for the QPOs in terms of standing sausage mode oscillations of flux tubes in the magnetar coronae. We show that most of the QPOs observed in SGR giant flares could be well accounted for except for those with very high frequencies (625 and 1840 Hz).