Quasi-periodic Variations in the Hard X-ray emission of a Large Arcade Flare

TL;DR

This paper investigates quasi-periodic oscillations in hard X-ray emissions during a large solar flare, revealing how magnetic trap oscillations and chromospheric evaporation influence electron acceleration and emission patterns.

Contribution

It provides observational evidence linking magnetic trap oscillations and chromospheric evaporation to HXR emission variations in solar flares, advancing understanding of flare dynamics.

Findings

Electrons are accelerated in oscillating magnetic traps within the cusp structure.

HXR pulse amplitudes increase with trap oscillation amplitude and plasma density.

Strong HXR pulses result from dense plasma inflow due to chromospheric evaporation.

Abstract

Quasi-periodic oscillations of the hard X-ray (HXR) emission of the large flare of 2 November 1991 have been investigated using HXR light curves and soft X-ray and HXR images recorded by the {\sl Yohkoh} X-ray telescopes. The results of the analysis of these observations are the following: i) The observations confirm that electrons are accelerated in oscillating magnetic traps which are contained within the cusp magnetic structure. ii) The amplitude of the HXR pulses increase due to the increase in the amplitude of the magnetic trap oscillations and the increase in the density within the traps caused by the chromospheric evaporation upflow. iii) The increase in the amplitude of the HXR pulses terminates when further increase in the density inside the traps inhibits the acceleration of electrons. iv) The model of oscillating magnetic traps is able to explain time variation of the electron precipitation, strong asymmetry in precipitation of accelerated electrons, and systematic differences in the precipitation of 15 and 25 keV electrons. v) We have obtained a direct observational evidence that strong HXR pulses are the result of the inflow of dense plasma coming from the chromospheric evaporation, into the acceleration volume.