Sparking Dynamic, Relativistic Magnetic Reconnection in a Twisted Flux Tube

Magnetic reconnection around neutron stars (NSs) forms small-scale currents while transferring energy to electron-positron pairs. These dissipating currents cover a wide range of scales, potentially leaving an imprint on time-variable X-ray bursts and pulsed radio emission. We present a reduced, planar model of internal reconnection in a magnetic flux tube with relativistic magnetization, finite resistivity, and strong guide field. Comparing with realistic NS parameters, this model represents the dynamics of a slender magnetic flux tube that is much thinner than the stellar radius. The seed current profile is smooth and does not spontaneously reconnect; instead, a discrete and localized current perturbation is introduced, representing e.g. localized energy release from a NS crust or magnetosphere. Three high-resolution relativistic magnetohydrodynamics simulations are described: one has uniform resistivity and Lundquist number such that reconnection proceeds in the plasmoid-mediated regime; the other two account for the feedback of charge starvation on the resistivity in current layers, where density is depleted; we provide a more general explanation for this depletion. All simulations produce a few dominant magnetic X-points and a secondary Kelvin-Helmholtz instability that excites high-wavenumber currents. We quantify the reconnection rate, the intermittency of dissipation, and the time profile of current spikes. We further present three-dimensional simulations confirming a limited growth of the ideal kink mode in the strong guide field regime. Applications are discussed, including to radio pulse microstructure and current damping below the magnetar surface during an X-ray flare, leading to mass loss and X-ray afterglow.