Lepton Acceleration by Relativistic Collisionless Magnetic Reconnection

We have calculated self-consistent equilibria of a collisionless relativistic electron-positron gas in the vicinity of a magnetic X-point. For the considered conditions, pertinent to extragalactic jets, we find that leptons are accelerated up to Lorentz factors Γ 0 = κ eB 0 L 2 / mc 2 ≫ 1, where B 0 is the typical magnetic field strength, ≡ E 0 / B 0 , with E 0 the reconnection electric field, L is the length scale of the magnetic field, and κ ≈ 12. The acceleration is due to the dominance of the electric field over the magnetic field in a region around the X-point. The distribution function of the accelerated leptons is found to be approximately dn / d γ ∝ γ -1 for γ ≲ Γ 0 . The apparent distribution function may be steeper than γ -1 due to the distribution of Γ 0 values and/or the radiative losses. Self-consistent equilibria are found only for plasma inflow rates to the X-point less than a critical value.