Pulsars are highly-magnetised rotating neutron stars and are well-known for the stability of their signature pulse shapes, allowing high-precision studies of their rotation. However, during the past 22 years, the radio pulse profile of the Crab pulsa
r has shown a steady increase in the separation of the main pulse and interpulse components at 0.62$^{rm o}pm$0.03$^{rm o}$ per century. There are also secular changes in the relative strengths of several components of the profile. The changing component separation indicates that the axis of the dipolar magnetic field, embedded in the neutron star, is moving towards the stellar equator. This evolution of the magnetic field could explain why the pulsar does not spin down as expected from simple braking by a rotating dipolar magnetic field.
We have simulated a population of young spin-powered pulsars and computed the beaming pattern and lightcurves for the three main geometrical models: polar cap emission, two-pole caustic (slot gap) emission and outer magnetosphere emission. The light
curve shapes depend sensitively on the magnetic inclination alpha and viewing angle zeta. We present the results as maps of observables such as peak multiplicity and gamma-ray peak separation in the (alpha, zeta) plane. These diagrams can be used to locate allowed regions for radio-loud and radio-quiet pulsars and to convert observed fluxes to true all-sky emission.
