Fast collisionless reconnection in electron-positron plasmas

Magnetic reconnection in electron-positron (pair) plasmas is studied by two-dimensional, electromagnetic, particle-in-cell simulations. In pair plasmas, the Hall current does not appear because there is no scale separation between ion and electron motion. Simulations show that fast reconnection is realized in both nonrelativistic and relativistic regimes. It is demonstrated that the divergence of the electron and positron pressure tensors essentially plays the role of an effective collisionless resistivity in realizing fast reconnection. Since there is no Hall current in pair plasmas, there is no quadrupolar structure in the out-of-plane magnetic field. Particle acceleration by reconnection is investigated. Major sites of particle acceleration are the regions in the vicinity of X lines, where ultrarelativistic particles are generated by the reconnection electric field.