Proton and electron acceleration by quasi-perpendicular fast magnetosonic shocks in interplanetary space

Abstract

Recent observations from the $\it Ulysses$ spacecraft (Simnett 2003, Sol. Phys., 213, 387) have measured the energy spectrum of the ambient ions associated with the passage of a fast magnetosonic quasi-perpendicular shock driven by a coronal mass ejection (CME). Near the shock front the energy spectrum of the accelerated ions, which are predominantly protons, exhibits features (maxima) at about 250 keV-1.5 MeV. We show that these are the right order of magnitude for protons which have been accelerated by the surfatron mechanism at a fast magnetosonic shock wave propagating perpendicular to the ambient magnetic field. The in situ measurements therefore illustrate directly that this mechanism could possibly be responsible for interplanetary particle acceleration. The shock is also accompanied by an increase in the near-relativistic electron intensity of almost two orders of magnitude. We present a similar event observed by the ACE spacecraft.