Precession of magnetars: dynamical evolutions and modulations on polarized electromagnetic waves
Gao, Yong
Magnetars are conceived to be highly magnetized neutron stars (NSs). Strong internal magnetic field and elasticity in the crust may deform the stars and lead to the precession of magnetars. We study the free precession of triaxially-deformed NSs and give the fully analytical solutions. Then we consider the forced precession problem by considering electromagnetic torques, including the anomalous torque and the spindown torque. The dynamical evolutions of the NS geometry are obtained in details. We apply those results to study the polarized radio and X-ray emissions that are modulated by precession. For radio signals, we give the timing residuals and the evolutions of the position angle in Rotating Vector Model (RVM). For the thermal X-ray coming from the surface of magnetars, we present the precession-modulated Stokes parameters for some specific photon energies. Our results are ready to be used to search the precession of magnetars. Observations of precessing magnetars will definitely give us valuable information on the geometry and the strength of the strong magnetic fields, the emission geometry and mechanism, as well as the EoS of NSs.