Power-law energy distributions of small-scale impulsive events on the active Sun: Results from IRIS

TL;DR

This study analyzes small-scale impulsive events on the Sun using IRIS data, revealing how their energy distribution varies with solar region and observational cadence, and assessing their role in coronal heating.

Contribution

It introduces a burst detection method to analyze power-law indices of impulsive events, highlighting regional and observational factors affecting energy distribution and their potential contribution to coronal heating.

Findings

Sunspot regions have power-law index γ < 2.

Plage regions often have γ > 2.

Impulsive events contribute 10-25% of the energy needed for coronal heating.

Abstract

Numerous studies have analysed inferred power-law distributions between frequency and energy of impulsive events in the outer solar atmosphere in an attempt to understand the predominant energy supply mechanism in the corona. Here, we apply a burst detection algorithm to high-resolution imaging data obtained by the Interface Region Imaging Spectrograph to further investigate the derived power-law index, $\gamma$, of bright impulsive events in the transition region. Applying the algorithm with a constant minimum event lifetime (of either $60$ s or $110$ s) indicated that the target under investigation, such as Plage and Sunspot, has an influence on the observed power-law index. For regions dominated by sunspots, we always find $\gamma <2$; however, for datasets where the target is a plage region, we often find that $\gamma >2$ in the energy range [$\sim10^{23}$, $\sim10^{26}$] erg. Applying the algorithm with a minimum event lifetime of three timesteps indicated that cadence was another important factor, with the highest cadence datasets returning $\gamma >2$ values. The estimated total radiative power obtained for the observed energy distributions is typically 10-25 % of what would be required to sustain the corona indicating that impulsive events in this energy range are not sufficient to solve coronal heating. If we were to extend the power-law distribution down to an energy of $10^{21}$ erg, and assume parity between radiative energy release and the deposition of thermal energy, then such bursts could provide 25-50 % of the required energy to account for the coronal heating problem.