Evidence for Electron Acceleration up to∼300 keVin the Magnetic Reconnection Diffusion Region of Earth’s Magnetotail
We report direct measurements of high-energy particles in a rare crossing of the diffusion region in Earth's magnetotail by the Wind spacecraft. The fluxes of energetic electrons up to $\ensuremath{\sim}300\text{ }\text{ }\mathrm{k}\mathrm{e}\mathrm{V}$ peak near the center of the diffusion region and decrease monotonically away from this region. The diffusion region electron flux spectrum obeys a power law with an index of $\ensuremath{-}3.8$ above $\ensuremath{\sim}2\text{ }\text{ }\mathrm{k}\mathrm{e}\mathrm{V}$, and the electron angular distribution displays strong field-aligned bidirectional anisotropy at energies below $\ensuremath{\sim}2\text{ }\text{ }\mathrm{k}\mathrm{e}\mathrm{V}$, becoming isotropic above $\ensuremath{\sim}6\text{ }\mathrm{k}\mathrm{e}\mathrm{V}$. These observations indicate significant electron acceleration inside the diffusion region. Ions show no such energization.