Waiting time distribution of solar energetic particle events modeled with a nonstationary Poisson process 

Chuan Li Submitted: 20140815 01:06
We present a study of the waiting time distributions (WTDs) of solar energetic particle (SEP) events observed with the spacecraft WIND and GOES. Both the WTDs of solar electron events (SEEs) and solar proton events (SPEs) display a powerlaw tail ~ Δ t^{\gamma}. The SEEs display a broken powerlaw WTD. The powerlaw index is \gamma_{1} = 0.99 for the short waiting times (<70 hours) and \gamma_{2} = 1.92 for large waiting times (>100 hours). The break of the WTD of SEEs is probably due to the modulation of the corotating interaction regions (CIRs). The powerlaw index \gamma ~ 1.82 is derived for the WTD of SPEs that is consistent with the WTD of type II radio bursts, indicating a close relationship between the shock wave and the production of energetic protons. The WTDs of SEP events can be modeled with a nonstationary Poisson process which was proposed to understand the waiting time statistics of solar flares (Wheatland 2000; Aschwanden & McTiernan 2010). We generalize the method and find that, if the SEP event rate \lambda = 1/Δ t varies as the time distribution of event rate f(\lambda) = A \lambda^{ α }exp(β \lambda), the timedependent Poisson distribution can produce a powerlaw tail WTD ~ Δ t^{ α  3}, where 0 ≤ α < 2.
Authors: Chuan Li, Sijia Zhong, Linghua Wang, Wei Su, and Cheng Fang
Projects: None

Publication Status: Accepted for publication in ApJ Letters
Last Modified: 20140820 09:47


