# Pulsar braking and the P-Pdot diagram

## TL;DR

This paper demonstrates that the decay of the inclination angle between magnetic and rotational axes significantly influences pulsar evolution in the P-Pdot diagram, challenging previous assumptions about magnetic field decay and initial periods.

## Contribution

It introduces a model incorporating inclination angle decay, showing it can explain pulsar distribution without assuming magnetic field decay or long birth periods.

## Key findings

- Reproduces the P-Pdot diagram with inclination angle decay
- Suggests a Galactic pulsar population of ~20,000
- Estimates a birth rate of 1 pulsar per century

## Abstract

The location of radio pulsars in the period-period derivative (P-Pdot) plane has been a key diagnostic tool since the early days of pulsar astronomy. Of particular importance is how pulsars evolve through the P-Pdot diagram with time. Here we show that the decay of the inclination angle (alpha-dot) between the magnetic and rotation axes plays a critical role. In particular, alpha-dot strongly impacts on the braking torque, an effect which has been largely ignored in previous work. We carry out simulations which include a negative alpha-dot term, and show that it is possible to reproduce the observational P-Pdot diagram without the need for either pulsars with long birth periods or magnetic field decay. Our best model indicates a birth rate of 1 radio pulsar per century and a total Galactic population of ~20000 pulsars beaming towards Earth.