Precession interpretation of the isolated pulsar PSR B1828-11

Pulse timing of the isolated pulsar PSR B1828-11 shows strong Fourier power at periods similar or equal to 1000, 500, and 250 days, correlated with ch anges in the pulse profile (Stairs, Lyne, & Shemar). We study the extent to which these data can be explained by precession of the star's rigid crust coupled to the magnetic dipole torque. We find that the correlated changes in the pulse duration and spin period derivative can be explained as preces sion at a period of similar or equal to 500 days with a wobble angle of sim ilar or equal to3 degrees if the star's dipole moment is nearly orthogonal to its symmetry axis. The dipole torque produces a harmonic at similar to 2 50 days. Comparison of the predicted spin dynamics with the observed pulse durations requires the radio beam to have a nonstandard "hourglass" shape. We make predictions of variations in beam polarization and pulse profile wi th which to test this interpretation. The precession interpretation of PSR B1828-11 seriously challenges the current understanding of the liquid inter ior of the neutron star. In particular, if the internal liquid is in a supe rfluid state, its rotational vortices cannot be significantly pinned to the crust.