Quasi-periodic pulsations with multiple periods in hard X-ray emission

Abstract

Abstract We explore quasi-periodic pulsations with multiple periods in hard X-ray (HXR) emission from the Fermi Gamma-ray Burst Monitor during the impulsive phase of a solar flare (SOL2014–09–10). The completely new observational result is that the shorter periods appear at lower energies of the X-ray photons at the beginning and the longer periods appear at higher energies at the end, with some intersection of the periods at medium energies. We also find shorter and then longer periods during the same phase of this flare. Using the wavelet power spectrum and fast Fourier transform spectrum, we analyse the normalized rapidly varying signal divided by its slowly varying signal, which is the smoothed original HXR flux. The periods of 27 and 37 s are derived at lower-energy channels between 17:25 and 17:29 ut (i.e. 12.0–27.3 and 27.3–50.9 keV). Then, the periods of 27, 46 and 60 s are observed at the medium-energy channel from 17:26 to 17:33 ut, such as 50.9–102.3 keV. Also, the period of 80 s is detected at the higher-energy channel from 17:28 to 17:33 ut, such as 102.3–296.4 keV.