Electron Kappa Distributions in Solar Flares and the Earth's Magnetotail

Explosive phenomena in the solar corona and the Earth's magnetotail produce non-thermal, energetic electrons of up to tens of MeV and hundreds of keV, respectively. While power-law energy spectra have been observed in both environments, similarities and differences of the power-law features remain unclear. Here we propose to use kappa distribution to compare the power-law spectral indices obtained by hard X-ray observations during solar flares as well as in-situ electron measurements in the Earth's magnetotail. We will present RHESSI solar flare observations in which foot-points of the flare loop were behind the solar limb so that the photon spectra of the hard X-ray coronal source could be studied without much contamination by photons from the foot-points. As a reference, we will also show a THEMIS observation of electron kappa distribution in the reconnection flow-braking region within the Earth's magnetotail.