Elementary Energy Release Events in Flaring Loops: Effects of Chromospheric Evaporation on X-rays

TL;DR

This paper models chromospheric evaporation in solar flaring loops, analyzing how energy release and electron acceleration influence X-ray emissions during different flare phases, with implications for understanding flare dynamics.

Contribution

It introduces a model linking energy release, electron acceleration, and evaporation in flaring loops, and proposes a method to apply this model to observational data for quantitative analysis.

Findings

HXRs dominate impulsive phase emission.

Thermal background affects HXR flux and spectral index correlation.

Model suggests a strategy for analyzing single-loop flare observations.

Abstract

With the elementary energy release events introduced in a previous paper (Liu & Fletcher 2009) we model the chromospheric evaporation in flaring loops. The thick-target hard X-ray (HXR) emission produced by electrons escaping from the acceleration region dominates the impulsive phase and the thin-target emission from the acceleration region dominates the low-energy thermal component in the gradual phase, as observed in early impulsive flares. Quantitative details depend on properties of the thermal background, which leads to variations in the correlation between HXR flux and spectral index. For lower temperature and/or higher density of the background electrons, the HXRs both rise and decay more quickly with a plateau near the peak. The plateau is less prominent at higher energies. Given the complexity of transport of mass, momentum, and energy along loops in the impulsive phase, we propose a strategy to apply this single-zone energy release and electron acceleration model to observations of flares associated with single loops so that the energy release, electron acceleration, and evaporation processes may be studied quantitatively.