Disk-Accreting Magnetic Neutron Stars as High-Energy Particle Accelerators

Abstract

AbstractInteraction 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.Subject headings: acceleration of particles — accretion, accretion disks — gamma rays: theory — plasmas — radiation mechanisms: nonthermal — stars: neutron