Determining Heating Rates in Reconnection Formed Flare Loops of the M8.0 Flare on 2005 May 13

TL;DR

This study models the energy release and plasma heating in flare loops during an M8.0 solar flare using multi-wavelength observations and the EBTEL model, providing new insights into energy deposition mechanisms.

Contribution

It introduces a method combining UV, X-ray, and spectral data to constrain heating in reconnection-formed flare loops, advancing understanding of energy release in solar flares.

Findings

Total flare loop heating energy estimated at 1.22e31 ergs.

Most plasma heating occurs in situ, not via beam-driven upflows.

Modeled emissions agree well with observations.

Abstract

We analyze and model an M8.0 flare on 2005 May 13 observed by TRACE and RHESSI to determine the energy release rate from magnetic reconnection that forms and heats numerous flare loops. The flare exhibits two ribbons in UV 1600 {\AA} emission. Analysis shows that the UV light curve at each flaring pixel rises impulsively within a few minutes, and decays slowly with a timescale >10 min. Since the lower atmosphere (transition region and chromosphere) responds to energy deposit nearly instantaneously, the rapid UV brightening is thought to reflect the energy release process in the newly formed flare loop rooted at the footpoint. We utilize spatially resolved (down to 1 arcsec) UV light curves and thick-target hard X-ray emission to construct heating functions of a few thousand flare loops anchored at UV foot points, and compute plasma evolution in these loops using the EBTEL model. The modeled coronal temperatures and densities of these flare loops are used to calculate synthetic soft X-ray spectra and light curves, which compare favorably with those observed by RHESSI and GOES/XRS. The time-dependent transition region DEM for each loop during its decay phase is also computed with a simplified model and used to calculate the optically-thin C IV line emission, which dominates the UV 1600 {\AA} bandpass during the flare. The computed C IV line emission decays at the same rate as observed. This study presents a method to constrain heating of reconnection-formed flare loops using all available observables independently, and provides insight into the physics of energy release and plasma heating during the flare. With this method, the lower limit of the total energy used to heat the flare loops in this event is estimated to be 1.22e31 ergs, of which only 1.9e30 ergs is carried by beam-driven upflows during the impulsive phase, suggesting that the coronal plasmas are predominantly heated in situ.