  A model is presented for the quasiperiodic component of magnetar emission
during the tail phase of giant flares. The model invokes modulation of the
particle number density in the magnetosphere. The magnetospheric currents are
modulated by torsional motion of the surface and we calculate that the
amplitude of neutron star surface oscillation should be ~1% of the NS radius in
order to produce the observed features in the power spectrum. Using an
axisymmetric analytical model for structure of the magnetosphere of an
oscillating NS, we calculate the angular distribution of the optical depth to
the resonant Compton scattering. The anisotropy of the optical depth may be why
QPO are observed only at particular rotational phases.
