The nearly 750 radio pulsars known so far are interpreted as rapidly spinning and strongly magnetized neutron stars which are radiating at the expense of rotational energy. For the cooling neutron stars we have plotted the luminosities derived for their non-thermal component. Assuming the standard picture of magnetic braking we find . The corresponding curves are indicated.
All pulsars lie close to the braking curves calculated for their respective polar magnetic fields.
The strong correlation suggests that the prime energy source of the X-ray emission is the pulsar's rotational energy. In particular the millisecond pulsars, which are separate from the majority of ordinary field pulsars, obey the same linear relationship with the same X-ray efficiency as the Crab type pulsars, indicating that their emission is mainly due to magnetospheric processes.