On the precession of the isolated pulsar PSR B1828-11
  Analysis of both pulse timing and pulse shape variations of the isolated pulsar PSR B1828-11 shows highly correlated and strong Fourier power at periods \~ 1000, 500, and 250 d (Stairs et al. 2000). The only description based on a free precession of star's rigid crust coupled to the magnetic dipole torque, explains the 500-component, as the fundamental Fourier frequency, with its harmonic 250-component (Link & Epstein 2001). In this paper, we show that if the dipole moment vector varies with time with a period nearly equal to the longest (probably fundamental) observed period (~ 1000 d), the dipole torque may produce the all other harmonics. We also find the second and fourth harmonics at periods ~ 500 and 250 d are dominant for small wobble angle ~ 3^o and large field's inclination angle 89^o. 
Vahid Rezania (Alberta, IASBS)