Particle acceleration in neutron star ultra-strong magnetic fields

Neutron stars produce ultra-relativistic particles efficiently accelerated by their ultra strong electromagnetic fields, copiously radiation very high energy photons in the GeV/TeV range. However, no numerical code is able to handle such very high Lorentz factors and magnetic field strengths around the quantum critical limit of \numprint{4.4e9}\SIunits{\tesla}. In this work, we study particle acceleration and radiation reaction damping in a magnetic dipole with magnetic field strengths as high as \numprint{e10}\SIunits{\tesla}, typical for magnetars. We investigated particle acceleration and the impact of radiation reaction for electrons, protons and iron nuclei. The maximum Lorentz factor depends on the particle species but only weakly on the magnetic field strength. Electrons reach energies up to $\gamma_e \approx \numprint{e8}-\numprint{e9}$ whereas protons energies up to $\gamma_p \approx \numprint{e5}-\numprint{e6}$ and iron up to $\gamma \approx \numprint{e4}-\numprint{e5}$. While protons and irons are not affected by radiation reaction, electrons are drastically decelerated, reducing their maximum Lorentz factor by 2 orders of magnitude.