Energetic particles and coronal mass ejections: a case study from ACE and ULYSSES

In 2001 the Ulysses spacecraft crossed the ecliptic plane near perihelion. The heliographic longitude with respect to the Earth was within +/- 20degrees. of the west solar limb while it was +/-15degrees of the ecliptic plane, which meant that coronal mass ejections seen off the solar west limb were likely to pass over Ulysses. On 10 May the largest > 38 keV electron intensity of the mission, since the Jovian encounter in 1992, was observed, which was accompanied by a fast perpendicular shock. This event was preceded by a fast coronal mass ejection some two and a half days earlier which is the probable source of the shock. However, both the ACE spacecraft and Ulysses observed, simultaneously, an intense, prompt electron event on 7 May from a solar flare associated with earlier coronal mass ejections also observed off the west limb; Ulysses was magnetically connected to a longitude well behind the west limb. ACE did not observe any ( at the 0.1% level) energetic electrons which were associated with the 10 May event seen at Ulysses. We discuss in detail the energetic particles seen at the two spacecraft during 7 - 11 May, with the objective of understanding the origin of the intense electron event seen on 10 May and the manner in which particles escaping from the shock populate the inner heliosphere. The energy spectrum of the ions at both ACE and Ulysses exhibits a maximum at around 400 keV; this form of the spectrum was seen at the shock itself. It appears that the strong shock driven by the fast coronal mass ejection is able to populate a large fraction of the inner heliosphere with accelerated ions. The shock-accelerated electrons do not pervade the inner heliosphere in the same manner as the ions. We suggest that the electron acceleration was enhanced by the presence of multiple coronal mass ejections.