An electron heating mechanism in the outflow region from the X-type neutral line

A linear analysis and 2 1/2-dimensional full-particle simulations are performed to investigate mechanisms of an electron heating due to a strong Hall current, which is caused by a large velocity difference between electrons and ions in the outflow region inside the diffusion region of the magnetic reconnection process. The numerical solution of the kinetic dispersion relation indicates that the prospective unstable mode varies according to the electron-ion relative velocity V_d; the kinetic cross-field streaming instability (KCSI) is dominant when V_d- is under the substantial fraction of the electron thermal velocity v_e, while the electron cyclotron drift instability (ECDI) is first excited for the case where V _d exceeds that critical velocity. We show that electrons are heated parallel to the ambient magnetic field due to the KCSI and perpendicularly due to the ECDI. In particular, electrons are very quickly heated up to a high temperature when the ECDI is dominant. However, the electron heating is ineffective when V_d/v_e < 1.