Nature of Interplanetary Low Energy Electrons and Positrons

We propose to explore the source of the negative spectral index of low energy cosmic ray electrons (20-100MeV). To accomplish this objective we will attack the problem from two fronts. First, we propose to measure electrons in the energy range of 20MeV to 300MeV with a new instrument, which we name AESOP-lite, on a high altitude balloon >140kft. This data will provide a clean, calibrated reference at 1AU to be compared with Voyager electron observations from interstellar space. Voyager I and II are currently returning electron spectra roughly within this energy range (<160MeV). Second, we plan to simultaneously measure the positron fraction in the electron flux within this low energy regime using the same instrument. Positron abundances in this energy range should be highly diagnostic of the particle origin. It is important to note these electron energies are not observable by the AMS and Pamela instruments. More »