Spin Evolution of Pulsars with Weakly Coupled Superfluid Interiors

We discuss the spin evolution of pulsars in the case where a superfluid component of the star is coupled to the observable crust on long, spin-down timescales. The momentum transfer from the superfluid interior results in an apparent decay of the external torque and, after a dramatic increase, in an asymptotic decrease of the generic value of the braking index, e.g., n = 3, to values n ~ 2.5 if the magnetic field of the star does not decay over its lifetime. In the case where an exponential decay of the magnetic field toward a residual value occurs, the star undergoes a spin-up phase after which it could emerge in the millisecond sector of the P-Ṗ diagram.