Entry of galactic electrons into the high latitude heliosphere

Abstract

Evidence is presented for the first detection of galactic cosmic ray electrons in the general energy range 1 to 20 MeV by the HI-SCALE instrument on Ulysses as it passed over the solar poles. The electrons manifest themselves by a strong latitude dependence of the background counting rates in the HI-SCALE detectors, in excess of that predicted from the COSPIN measurements. The majority of the detected electrons have penetrated the housing around the detectors; the apparent spectrum of this excess is completely inconsistent with penetrating ions, whatever their spectrum. We have compared the inferred electron flux with an extrapolation of the cosmic ray electron spectrum measured in the ecliptic plane and inferred from radio astronomy at ≳1 GeV and conclude that the galactic spectrum does not continue as a power law down to a few MeV.