2017MNRAS.467.3493J

The location of radio pulsars in the period-period derivative (P-{dot}P) plane has been a key diagnostic tool since the early days of pulsar astronomy. Of particular importance is how pulsars evolve through the P-{dot}P diagram with time. Here we show that the decay of the inclination angle ({dot}α) between the magnetic and rotation axes plays a critical role. In particular, {dot}α strongly impacts on the braking torque, an effect that has been largely ignored in previous work. We carry out simulations that include a negative {dot}α term, and show that it is possible to reproduce the observational P-{dot}P diagram without the need for either pulsars with long birth periods or magnetic field decay. Our best model indicates a birth rate of one radio pulsar per century and a total Galactic population of ∼20 000 pulsars beaming towards Earth.