Evidence of thermal conduction suppression in hot coronal loops: Supplementary results

TL;DR

This study investigates thermal conduction suppression in hot coronal loops during solar flares, finding that nonlocal conduction effects explain slower cooling rates and suggest larger flares may be hotter than previously predicted.

Contribution

It introduces an alternative method to determine the polytropic index, confirming conduction suppression without linear approximation assumptions.

Findings

Flare loops cool 2-4 times slower than classical models predict.

Nonlocal conduction approximation aligns with observed cooling times.

Larger flares may be hotter than traditional EM-T relations suggest.

Abstract

Slow magnetoacoustic waves were first detected in hot ($>$6 MK) flare loops by the SOHO/SUMER spectrometer as Doppler shift oscillations in Fe XIX and Fe XXI lines. Recently, such longitudinal waves have been found by SDO/AIA in the 94 and 131 \AA\ channels. Wang et al. (2015) reported the first AIA event revealing signatures in agreement with a fundamental standing slow-mode wave, and found quantitative evidence for thermal conduction suppression from the temperature and density perturbations in the hot loop plasma of $\gtrsim$ 9 MK. The present study extends the work of Wang et al. (2015) by using an alternative approach. We determine the polytropic index directly based on the polytropic assumption instead of invoking the linear approximation. The same results are obtained as in the linear approximation, indicating that the nonlinearity effect is negligible. We find that the flare loop cools slower (by a factor of 2-4) than expected from the classical Spitzer conductive cooling, approximately consistent with the result of conduction suppression obtained from the wave analysis. The modified Spitzer cooling timescales based on the nonlocal conduction approximation are consistent with the observed, suggesting that nonlocal conduction may account for the observed conduction suppression in this event. In addition, the conduction suppression mechanism predicts that larger flares may tend to be hotter than expected by the EM-$T$ relation derived by Shibata & Yokoyama (2002)