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

## TL;DR

This study identifies multiple quasi-periodic pulsations in solar flare hard X-ray emissions, revealing energy-dependent period variations and their evolution during the flare's impulsive phase.

## Contribution

It provides the first observational evidence of energy-dependent QPPs with multiple periods in solar flare HXR emissions, analyzed through wavelet and FFT methods.

## Key findings

- Shorter periods at lower energies at the flare start
- Longer periods at higher energies at the flare end
- Multiple periods observed during the same phase

## Abstract

We explore the quasi-periodic pulsations (QPPs) with multiple periods in hard X-ray (HXR) emission from Fermi/GBM during the impulsive phase of 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 the shorter and then the longer periods during the same phase of this flare. Using the wavelet power spectrum and fast Fourier transform (FFT) spectrum, we analyze the normalized rapidly varying signal divided by its slowly varying signal, which is the smoothed original HXR flux. The periods of 27 s and 37 s are derived at lower energy channels between 17:25 UT and 17:29 UT, i.e., 12.0-27.3 keV and 27.3-50.9 keV. Then the periods of 27 s, 46 s and 60 s are observed at medium-energy channel from 17:26 UT to 17:33 UT, such as 50.9-102.3 keV. And the period of 80 s is detected at higher energy channel from 17:28 UT to 17:33 UT, such as 102.3-296.4 keV.