Princeton University Astroplasmas Seminar

In contrast with radio pulsars, the electric current flowing outside a magnetar can approach in strength the internal current supporting its magnetic field. Obtaining a self-consistent description of this circuit is a pre-requisite for understanding the unusual X-ray, infrared and radio emission and extreme torque variability of Galactic magnetars, and the plasma state at the onset of a giant flare or fast radio burst. We show that the interactions of electrons, positrons and photons are modified in some significant ways in the presence of a super-QED magnetic field. Collisionality of a pair plasma is strongly enhanced by single-photon pair annihilation and re-conversion; two-photon pair annihilation develops a soft, bremsstrahlung-like spectral tail; electron-photon scattering shows a new resonance in the recoil-dominated regime; and the cross section for photon collisions is dramatically enhanced. A Monte Carlo implementation of these processes reveals a novel collisional state in which hard X-ray emission similar to that observed is balanced by ohmic heating in narrow flux bundles that may be connected with fault-like features in the magnetar crust.