On the Lower Energy Cutoff of Nonthermal Electrons in Solar Flares

1 INTRODUCTIONThe lower energy cutoff of nonthermal electron beams is an important quantity. Not only isit related to the acceleration mechanism, but it also determines the total number of acceleratedelectrons and the energy they carry. The power-law of electron beams cannot extend to lowerenergies indefinitely for if it did, it would imply an indeflnite1y large nuInber of electrons.A lower energy cutoff (E.), therefore, must exist, to keep the number of electrons within areasonable rang…

On the Lower Energy Cutoff of Nonthermal Electrons in Solar Flares

A quantitative method to determine the lower energy cutoff (Ec) of power-lay electron beams is established. We apply this method to the 54 hard X-ray events observed with BATSE/Compton Gamma Ray Observatory (CGRO). The results show that about 75% of the observed broken double power-law electron beams. The values of Ec, vrying among the flares, are all greater than the usually accepted 20keV! On average, Ec is about 69keV. So high a lower energy cutoff of nonthermal electrons implies that nonthermal electrons might not be as important in powering solar flares as was previously thought. Further significance of this finding is discussed.