On the origin of corotating energetic particle events

Energetic corotating particle events could be produced by acceleration at the forward and reverse shock pair, which bounds a corotating interaction region, via the process of successive multiple reflections. In the steady state, which should be the situation applicable to corotating events, the energetic particle intensity at the shock depends only on the acceleration strength of the shock and on the intensity of the source particles. Measurements of energetic particles show systematic variations: intensities at the forward shock are typically smaller than those at the reverse shock and increase with heliocentric distance (between ∼1 and 5 AU), whereas intensities at the reverse shock tend to decrease with heliocentric distance. Since there is no obvious difference between forward and reverse shock strengths, the origin for this behavior could lie in the particle source. Assuming that this source is part of the solar wind plasma and that the solar wind temperature is the best available indicator for the intensity of these particles, it is argued that a correlation between energetic particle intensities and plasma temperature should exist. Detailed analysis of individual events, as well as a statistical analysis, yields such a correlation. This suggests that the solar wind is the original particle population that is accelerated in the stationary shocks up to several MeV.