Time-to-Maximum Studies and Inferred Ionic Charge States in the Solar Energetic Particle Events of 14 and 15 April 2001

摘要

We have used data from Wind,ACE,IMP8,and GOES to determine the time-to-maximum (TTM) intensity in the solar energetic particle (SEP) events of 14 and 15 April 2001.(The former event was one of the largest impulsive events of Cycle 23,while the later was the largest ground-level event of the Cycle.) From the apparent rigidity-ordering of the TTMs we infer the mean ionic charge state of Fe.In the 14 April event,the analysis indicates that Fe is fully stripped.But in the 15 April event,the charge state increases with energy,in agreement with the observations at ~1 MeV/nuc and at ~30 MeV/nuc from SAMPEX.This study shows that reliable ionic charge states can be inferred from the TTM method,thus providing a tool for studying charges states at intermediate energies for which no direct measurements are available.