Pulsar twinkling and relativity

The number of pulsars with detected emission at X-ray and γ-ray energies has been steadily growing, showing that beams of high-energy particles are commonly accelerated in pulsar magnetospheres, even though the location and number of acceleration sites remain unsettled. Acceleration near the magnetic poles, close to the polar cap surface or to higher altitudes in the slot gap along the last open £eld lines, involves an electric £eld component due to inertial-frame dragging. Acceleration can also take place in the outer magnetosphere where charge depletion due to global currents causes a large electric £eld along the magnetic £eld lines. All models require a detailed knowledge of the open magnetosphere geometry and its relativistic distortions. Observational trends with age, spin-down power and magnetic £eld as well as population synthesis studies in the Galactic disc and the nearby Gould Belt provide useful, however not yet conclusive, constraints on the competing models.