Interpreting the Spin-down Evolutions of Isolated Neutron Stars with Hall Effects

Abstract: The observed long-term spin-down evolution of isolated radio pulsars cannot be explained by the standard magnetic dipole radiation with a constant braking torque. However, how and why the torque varies still remains controversial, which is a major issue in understanding neutron stars. Many pulsars have been observed with significant long-term changes of their spin-down rates modulated by quasi-periodic oscillations. Applying the phenomenological model of pulsar timing noise we developed recently to the observed precise pulsar timing data of isolated neutron stars, here we show that the observed long-term evolutions of their spin-down rates and quasi-periodic modulations can be explained by Hall effects in their crusts. Therefore the evolution of their crustal magnetic fields, rather than that in their cores, dominates the observed long term spin-down evolution of these young pulsars. Understanding of the nature of pulsar timing noise not only reveals the interior physics of neutron stars, but also allows physical modeling of pulsar spin-down and thus improves the sensitivity of gravitational wave detections with pulsars.