Energetic Particles Associated with the Interplanetary Shock of 25 September 2001

We report on the elemental abundances of energetic particles associated with an interplanetary shock which passed the Advanced Composition Explorer (ACE) spacecraft at ∼ 20:05 UT on 25 September 2001. The shock is associated with a solar X-ray event (X2.6) at S16E23 on 24 September at ∼ 10:38 UT. This corresponds to an average speed of 1232 km/sec to reach 1 AU. Heavy elements above 14 MeV/nucleon were observed from He to Fe. The time-intensity profile for He is that of a classic Energetic Storm Particle event, i.e. there is a shock-associated increase riding on top of a solar particle event profile. This increase is ∼ 12 hours wide and peaks ∼ 6 to 8 hours after the shock arrival. What is unusual about this event is that the time-intensity profiles of O and Fe are considerably different from the He profile. This event illustrates some of the difficulties in relating observations to current models of shock acceleration. This research was supported by NASA at the Goddard Space Flight Center, the California Institute of Technology (under Grant NAG5-12929), and the Jet Propulsion Laboratory.