Electromagnetic torques, secular alignment, and spin-down of neutron stars

The authors study the electromagnetic torques on a rotating neutron star (radius a, magnetic moment M, angular frequency Ω), including both vacuum (retardation) effects and those caused by current flowing in the magnetosphere. The dipole is taken to be inclined with respect to the rotation axis, and effects of both dipole and quadrupole moments are included. It is found (1) that there are several dipole torque terms, incalculable at present, of the same order of magnitude as the classical vacuum dipole torque and (2) that there are "anomalous" torques ≡ (c/Ωa) times larger than the classical one, but which do not affect either the spin-down rate or the alignment for a rigid-sphere dipole.