A simple estimate for the energies of electrons accelerated in flare current sheets on the sun

Abstract

A major result from Yohkoh is the frequency with which hard X-ray sources occur above solar flare loops. Observations suggest that electron acceleration in flares occurs in the magnetic reconnection region above the loops. Unfortunately, models for particle acceleration in reconnecting current sheets predict electron energy gains in terms of the reconnection electric field and the thickness of the sheet, both of which are extremely difficult to measure. It can be shown, however, that application of Ohm's law in a turbulent current sheet, combined with energy and Maxwell's equations, leads to a formula for the electron energy gain in terms of the flare power output, the magnetic field strength, the plasma density and temperature in the sheet, and its area. Typical flare parameters correspond to electron energies between a few tens of keV and a few MeV.