The Weibull functional form for the energetic particle spectrum at interplanetary shock waves

[摘要] Transient interplanetary shock waves are often associated with high energy particle enhancements, which are called energetic storm particle (ESP) events. Here we present a case study of an ESP event, recorded by the SEPT, LET and HET instruments onboard the STEREO B spacecraft, on 3 October 2011, in a wide energy range from 0.1 MeV to ∼ 30 MeV. The obtained particle spectrum is found to be reproduced by a Weibull like shape. Moreover, we show that the Weibull spectrum can be theoretically derived as the asymptotic steady state solution of the diffusion loss equation by assuming anomalous diffusion for particle velocity. The evaluation of Weibull's parameters obtained from particle observations and the power spectral density of the turbulent fluctations in the shock region, support this scenario and suggest that stochastic acceleration can contribute significantly to the acceleration of high energetic particles at collisioness shock waves.

[发布机构] INAF-Istituto di Astrofisica e Planetologia Spaziali, Roma, Italy^1;Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan^2

[效力级别] 天文学 [学科分类] 天文学(综合)

[关键词] Anomalous diffusion;Asymptotic steady state;Energetic particles;High-energy particles;Interplanetary shock waves;Particle velocities;Stochastic acceleration;Wide energy range