Disk-accreting magnetic neutron stars as high-energy particle accelerators

Interaction of an accretion disk with the magnetic field of a neutron star produces large electromotive forces, which drive large conduction currents in the disk-magnetosphere-star circuit. Here we argue that such large conduction currents will cause microscopic and macroscopic instabilities in the magnetosphere. If the minimum plasma density in the magnetosphere is relatively low (≲10⁹ cm^-3), current-driven micro-instabilities may cause relativistic double layers to form, producing voltage differences in excess of 10¹² V and accelerating charged particles to very high energies. If instead the plasma density is higher (≳10⁹ cm^-3), twisting of the stellar magnetic field is likely to cause magnetic field reconnection. This reconnection will be relativistic, accelerating plasma in the magnetosphere to relativistic speeds and a small fraction of particles to very high energies. Interaction of these high-energy particles with X-rays, γ-rays, and accreting plasma may produce detectable high-energy radiation.