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 $\simeq$1000, 500, 250, and 167 d (Stairs et al. [CITE]). The only description based on a free precession of the star's rigid crust coupled to the magnetic dipole torque, explains the 500 d-component, as the fundamental Fourier frequency, with its harmonic 250 d-component (Link & Epstein [CITE]). In this paper, we study a time-varying magnetic field model and show that if the dipole moment vector rotates with a period nearly equal to the longest (assumed fundamental) observed period ($\simeq$1000 d) relative to the star's body axes, the resulting magnetic torque may produce the whole Fourier spectrum consistently. We also find the second and fourth harmonics at periods $\simeq$500 and 250 d are dominant for small wobble angle $\simeq$ $3^\circ$ and large field's inclination angle ≥ $89^\circ$. We note that, although our model simply explains the observed pulse timing and pulse shape variations of PSR B1828-11, it also evokes some serious problems with our currently understanding from the physics of the neutron star structure