Electron-Scale Front of Magnetic Pile-Up Region in Reconnection Exhaust

The magnetic pile-up region and its front, which plays a crucial role in electron energization during magnetic reconnection, has been widely studied at fluid and ion scales. However, there have been few studies on electron-scale front of magnetic pile-up regions so far. Here, we present detailed observations of electron-scale front in a tailward reconnection exhaust. With a thickness of-5.5 de (electron inertial length), the front propagated along its normal direction, mainly along the reconnection outflow direction. At this front, the strong energy conversion observed was mainly driven by the perpendicular electron current. The front can lead to adiabatic electron heating and acceleration. The front hosts an intense and highly structured electric field, reaching up to-120 mV/m and predominantly attributed to the electron convection term. Electrostatic waves with frequencies higher than the electron gyrofrequency and parallel normal angles (WRT background magnetic field) were detected adjacent to the front. Our study can provide insight into the roles of fronts and electron-scale physics in magnetic reconnection.