Distribution of apparent beamwidths of pulsars and evolution of their magnetic inclinations

We analyse the distribution of the apparent beamwidth in a sample of 195 pulsars with known ages. Assuming the polar cap model, we derive the expression for the conditional density of α at given magnetic inclination φ. We then derive the frequency distribution of φ in each of four age groups. We find the distribution shows a preference for small values, 73% of the total having φ ≤ 30°. There is also a tendency for φ to decrease with age.