Spacecraft observations and analytic theory of crescent-shaped electron distributions in asymmetric magnetic reconnection

TL;DR

This paper combines spacecraft observations and kinetic simulations to develop an analytic model explaining crescent-shaped electron distributions during asymmetric magnetic reconnection, highlighting the role of an exclusion energy parameter in electron crossing behavior.

Contribution

The study introduces a new analytic model with an exclusion energy parameter that explains crescent-shaped electron distributions observed in asymmetric reconnection.

Findings

Identification of an exclusion energy parameter $\\cal{E}_X$ for electron crossing

Analytic explanation for crescent-shaped electron distributions

Validation with spacecraft observations and kinetic simulations

Abstract

Supported by a kinetic simulation, we derive an exclusion energy parameter $\cal{E}_X$ providing a lower kinetic energy bound for an electron to cross from one inflow region to the other during magnetic reconnection. As by a Maxwell Demon, only high energy electrons are permitted to cross the inner reconnection region, setting the electron distribution function observed along the low density side separatrix during asymmetric reconnection. The analytic model accounts for the two distinct flavors of crescent-shaped electron distributions observed by spacecraft in a thin boundary layer along the low density separatrix.