Evidence for Electron Acceleration up to ~300 keV in the Magnetic Reconnection Diffusion Region of the Earth's Magnetotail

We report direct measurements of high energy particles in a rare crossing of the diffusion region in the Earth's magnetotail by the Wind spacecraft. The fluxes of energetic electrons up to ~300 keV peak near the center of the diffusion region and decrease monotonically away from this region. The electron flux spectrum obeys a power law with an index of -3.8 above ~2 keV, and the electron angular distribution displays strong field-aligned bi-directional anisotropy at energies below ~2 keV, becoming isotropic above ~6 keV. These observations indicate significant electron acceleration inside the diffusion region. Ions show no such energization.