||Hall Drift in the Crust of Neutron Stars — Necessary for Radio Pulsar Activity?
||466, Electromagnetic Radiation from Pulsars and Magnetars
||Geppert, U.; Gil, J.; Melikidze, G.; Pons, J.; Viganò, D.
||The radio pulsar models based on the existence of an inner accelerating gap
located above the polar cap rely on the existence of a small scale, strong
surface magnetic field Bs. This field exceeds the dipolar field Bd,
responsible for the braking of the pulsar rotation, by at least one order
of magnitude. Neither magnetospheric currents nor small scale field
components generated during neutron star birth can provide such field
structures in old pulsars. While the former are too weak to create
Bs > 5 × 1013G ≫ Bd, the ohmic decay time of the
latter is much shorter than 106 years.
We suggest that a large amount of magnetic energy is stored in a toroidal
field component that is confined in deeper layers of the crust, where the
ohmic decay time exceeds 107 years. This toroidal field may be created
by various processes acting in the early stage of a neutron star's life. The Hall drift
is a non-linear mechanism that, due to the coupling between different
components and scales, may be able to create the demanded strong, small
scale, magnetic spots.
Taking into account both realistic crustal microphysics and a minimal
cooling scenario, we show that, in axial symmetry, these field structures
are created on a Hall time scale of 103 – 104 years. These magnetic
spots can be long-lived, thereby fulfilling the pre-conditions for the
appearance of the radio pulsar activity. Such magnetic structures created
by the Hall drift are not static, and dynamical variations on the Hall time
scale are expected in the polar cap region.