Nonaxisymmetric Precession of Magnetars and Fast Radio Bursts

The repeating FRBs 180916.J0158 and 121102 are visible during periodically-occuring windows in time. We consider the constraints on internal magnetic fields geometry if cyclical behavior observed for FRB~180916.J0158 FRB is due to precession of magnetars. In order frustrate vortex line pinning we argue that must be stronger than about $10^{16}$ Gauss, which large enough prevent superconductivity core destroy crustal lattice structure. conjecture field inside precessing magnetars has three components, (1) a dipole component with characteristic strength $\sim 10^{14}$ Gauss; (2) toroidal 10^{15}-10^{16}$ Gauss only occupies modest fraction stellar volume; (3) disordered 10^{16}$ Gauss. primarily responsible permitting precession, stops once this decays away, happens after 1000$ years. Conceivably, as damps bursting activity diminishes eventually ceases. model quadrupolar distortion star, its ordered components primarily, triaxial very likely prolate. address question whether or not spin frequency ought detectable precessing, by constructing specific bursts happen randomly time random directions distributed between cones relative single symmetry axis. Within context these models, find there geometries detecting unlikely.