Periodicity of ~155 days in solar electron fluence

In this paper we have investigated the occurrence rate of high energetic(E>10 MeV) solar electron flares measured by IMP-8 spacecraft of NASA for solar cycle 21 (June, 1976 to August, 1986) first time by three different methods to detect periodicities accurately. Power-spectrum analysis confirms a periodicity ~155 days which is in consistent with the result of Chowdhury and Ray (2006), that "Rieger periodicity" was operated throughout the cycle 21 and it is independent on the energy of the electron fluxes.