Quasi-periodic pulsations in hard X-rays of partially occulted solar flares

摘要

We investigated solar flares partially occulted by the solar disk observed by the Yohkoh satellite. We found that about 30-40% of them show quasi-periodic pulsations (QPPs) in hard X-rays (HXR). A lack of usually brighter footpoint sources allowed us to reconstruct coronal HXR sources with a higher quality. We analyzed 28 partially occulted flares showing the QPPs and for the first time present results for such events as a group. In our opinion, the majority of the observed HXR loop-top sources can be explained as successive compression and rarefaction of magnetic traps described in a model of oscillating magnetic traps (OMT). In this model a particular value of a ratio between the diameter of traps and the period of pulsations is postulated. In our modification of this model, different values of the ratio are possible, with the exception of a lower range, where low values of magnetic field strength and high values of electron density number can excess the plasma-beta parameter above unity (ballooning instability). (C) 2019 COSPAR. Published by Elsevier Ltd. All rights reserved.