Energetic water group ion fluxes (E_H2O greater than 60 keV) in a quasiperpendicular and a quasiparallel shock front as observed during the Giotto-Halley encounter

Abstract

Energetic water-group ions recorded by the Energetic Particle Analyzer/Energetic Particle Onset Admonitor (EPA/EPONA) and the Johnstone Plasma Analyzer (JPA) experiment aboard Giotto, as well as corresponding magnetic field measurements obtained, especially at the quasi-perpendicular inbound and quasi-parallel outbound bow shocks of Comet Halley, were used to study particle propagation and acceleration processes in the bowshock environment. It was found that energetic particles were accelerated in association with a strong magnetosonic wave field in the foreshock, in the inbound bowshock, within the near cometosheath, as well as immediately inside and outside the broad outbound bowshock. A relatively hard spectrum was observed in the inbound foreshock. Inside the bowshock itself, the spectrum was somewhat softer due to an increase in the fluxes in the lowest energy channels. Further acceleration of the particles took place inside the cometosheath. First- and second-order Fermi processes, as well as the transit time damping effect were most likely to have been responsible for particle acceleration at and within the bowshocks of Comet Halley.