In situ evidence of electron energization in the electron diffusion region of magnetotail reconnection

Magnetic reconnection is an explosive energy-release process in laboratory, space, and astrophysical plasmas. While magnetic fields can break and reconnect in a very small region called the electron diffusion region (EDR), there have been conflicting theories as to whether this region can be a place of rapid energization of plasmas. Here we report a fortuitous encounter of the EDR by The Time History of Events and Macroscale Interactions during Substorms (THEMIS) in the Earth's magnetotail where significant heating and demagnetization of electrons were observed. Additional energization was observed on both sides (immediate upstream and downstream) of the EDR, leading to a total of more than an order of magnitude energization across this region. The results demonstrate that despite its minuscule size, the EDR does indeed contribute to the overall process of electron energization via magnetic reconnection.