Precession Interpretation of the Isolated Pulsar PSR B1828−11

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Abstract
Pulse timing of the isolated pulsar PSR B1828-11 shows strong Fourier power at periods 1000, 500, and 250 days, correlated with changes 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 precession at a period of 500 days with a wobble angle of 3° if the star's dipole moment is nearly orthogonal to its symmetry axis. The dipole torque produces a harmonic at ~250 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 with which to test this interpretation. The precession interpretation of PSR B1828-11 seriously challenges the current understanding of the liquid interior of the neutron star. In particular, if the internal liquid is in a superfluid state, its rotational vortices cannot be significantly pinned to the crust.
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