  We compute the characteristic parameters of magnetic dipole radiation of a
neutron star undergoing torsional seismic vibrations under the action of
Lorentz restoring force about axis of a dipolar magnetic field experiencing
decay. After brief outline of general theoretical background of the model of
vibration powered neutron star, we present numerical estimates of basic
vibration and radiation characteristics, such as the oscillation frequency,
lifetime, luminosity of radiation, and investigate their time dependence upon
magnetic field decay. The presented analysis suggests that gradual decrease in
frequencies of pulsating high-energy emission detected from a handful of
currently monitored AXP/SGR-like X-ray sources can be explained as being
produced by vibration powered magneto-dipole radiation of quaking magnetars.
  \keywords{neutron stars, torsion Alfv\'en vibrations, vibration powered
radiation, magnetic field decay, magnetars}
