Investigation of quasi-periodic varaiations in hard X-rays of solar flares

TL;DR

This paper investigates quasi-periodic oscillations in hard X-rays of solar flares to understand electron acceleration, proposing a magnetic trap oscillation model that explains observed periodicities and acceleration impulses.

Contribution

It introduces a model of oscillating magnetic traps to explain quasi-periodic HXR oscillations and electron acceleration in solar flares, supported by observational correlations.

Findings

Good correlation between oscillation periods and loop-top source sizes.

Oscillating magnetic traps can explain impulsive electron acceleration.

Model accounts for quasi-periodic distribution of accelerated electrons.

Abstract

The aim of the present paper is to use quasi-periodic oscillations in hard X-rays (HXRs) of solar flares as a diagnostic tool for investigation of impulsive electron acceleration. We have selected a number of flares which showed quasi-periodic oscillations in hard X-rays and their loop-top sources could be easily recognized in HXR images. We have considered MHD standing waves to explain the observed HXR oscillations. We interpret these HXR oscillations as being due to oscillations of magnetic traps within cusp-like magnetic structures. This is confirmed by a good correlation between periods of the oscillations and the sizes of the loop-top sources. We argue that a model of oscillating magnetic traps is adequate to explain the observations. During the compressions of a trap particles are accelerated, but during its expansions plasma, coming from chromospheric evaporation, fills the trap, which explains the large number of electrons being accelerated during a sequence of strong impulses. The advantage of our model of oscillating magnetic traps is that it can explain both the impulses of electron acceleration and quasi-periodicity of their distribution in time.