Effects of crustal ohmic dissipation and alignment

We investigate the evolution of pulsars in the (P, Ṗ ) diagram. We first present analytical formulae to follow the evolution of a pulsar using simple exponential models for magnetic field decay and alignment. We then compare these evolutionary tracks with detailed model calculations using ohmic decay of crustal neutron star magnetic fields. We find that, after an initial phase with a small braking index, n, pulsars evolve with enhanced torque decay (n ≫ 3) for a short interval of time (0.1− 1 Myr) before returning to a long term n ≈ 3 evolution. Hence, we expect the true age of relatively old pulsars to be approximately equal to their observed characteristic age, τ = P/(2Ṗ ). It is not possible from data to constrain model parameters of the neutron star crust.