ar X iv : a st ro - p h / 02 05 18 0 v 3 2 9 Ju l 2 00 2 On the precession of the isolated pulsar PSR B 1828 - 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, 250, and 167 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 magnetic dipole torque may produce the all other harmonics. We find the second and fourth harmonics at periods ≃ 500 and 250 d are dominant for small wobble angle ≃ 3 and large field’s inclination angle & 89. Further, in a good agreement with data, we model the changes of the pulse shape in the precession cycle and find that the variation of pulse duration follows from a standard beam pattern in this cycle. Subject headings: pulsar: individual(PSR B1828-11) – stars: neutron – stars: magnetic fields