Timing noise in pulsars and magnetars and the magnetospheric moment of inertia

We examine timing noise in both magnetars and regular pulsars, and find that there exists a component of the timing noise (σTN) with strong magnetic field dependence (\sigma _TN \sim B_o^{2} \Omega T^{3/2}) above Bo ~ 1012.5 G. The dependence of the timing noise floor on the magnetic field is also reflected in the smallest observable glitch size. We find that magnetospheric torque variation cannot explain this component of timing noise. We calculate the moment of inertia of the magnetic field outside of a neutron star and show that this timing noise component may be due to variation of this moment of inertia, and could be evidence of rapid global magnetospheric variability.