Creation of magnetic spots at the neutron star surface

TL;DR

This paper explores how magnetic spots on neutron star surfaces, crucial for pulsar activity, can form through Hall drift extracting energy from deep crustal toroidal magnetic fields, with implications for their observability and longevity.

Contribution

It demonstrates that magnetic spots can form within 10^4 years via Hall drift from deep crustal toroidal fields, highlighting conditions for their creation and persistence.

Findings

Magnetic spots form within 10^4 years if toroidal fields are strong enough.

The lifetime of magnetic spots exceeds one million years under certain conditions.

Formation depends on the magnetic energy stored in the toroidal component and crust conductivity.

Abstract

According to the partially screened gap scenario, an efficient electron-positron pair creation, a general precondition of radio-pulsar activity, relies on the existence of magnetic spots, i.e., local concentrations of strong and small scale magnetic field structures at the surface of neutron stars. They have a strong impact on the surface temperature, which is potentially observable. Here we reinforce the idea that such magnetic spots can be formed by extracting magnetic energy from the toroidal field that resides in deep crustal layers, via Hall drift. We study and discuss the magneto-thermal evolution of qualitatively different neutron star models and initial magnetic field configurations that lead to the creation of magnetic spots. We find that magnetic spots can be created on a timescale of $10^4$ years with magnetic field strengths $\gtrsim 5\times 10^{13}$ G, provided almost the whole magnetic energy is stored in its toroidal component, and that the conductivity in the inner crust is not too large. The lifetime of the magnetic spots is at least $\sim$one million of years, being longer if the initial field permeates both core and crust.