Suparthermal electron strahl widths in the presence of whistler waves in the solar wind

Abstract:

Suprathermal electrons (E ~70eV-2keV) in the pristine solar wind are comprised of two populations: a halo and a field aligned, antisunward propagating strahl. In the past it has been shown that suprathermal electron population must exist already in the solar corona, but should be focused in a very narrow beam due to the effect of the diverging interplanetary magnetic field in the interplanetary space. However the observations show much wider strahl and the presence of approximately isotropic halo. It has been speculated in the past that the finite strahl widths and the halo itself are formed due to scattering of the strahl electrons by sunward propagating whistler waves. In this work we perform a statistical study of the interaction of the strahl electrons with whistler waves by comparing the average strahl widths during times of pristine solar wind in the presence and absence of these waves at different electron energies. We find that the whistler waves may cause widening of the electron strahl, but only in a limited range of electron energies, between ~200eV and 530eV. We discuss our findings in terms of possible instabilities that may cause the whistler waves to appear and resonantly interact with the electrons.