Slide 48 of 59
Notes:
Pulses from the rotating neutron star are only observed when the beam points at the Earth, ie for those pulsars whose magnetic axis lies close to the pulsar-Earth line of sight.
One difficulty with this idea is that despite differences in character (ie whether coherent or not) of radiation mechanisms at different frequencies, all of them must provide the same orientation of radiation along the magnetic field.
The source of radiation is probably localized inside the light cylinder, rather close to the surface of the neutron star and this is for two reasons : a) the stability of the pulses indicates that there is little opportunity for the emission region to wander about it’s mean position: and b) the high degree of directionality of the radiation suggests that it is produced in a region where the field lines are not greatly dispersed in direction and this is true near the surface.