Flarelike brightenings of active region loops observed with SUMER

TL;DR

This study analyzes frequent small flare-like brightenings in active region loops observed by SUMER, finding their energies and durations, and exploring their potential role in heating the solar corona.

Contribution

It provides a detailed statistical analysis of small brightenings in active region loops and assesses their possible contribution to coronal heating, using SUMER and Yohkoh data.

Findings

Brightenings last 5-84 minutes and extend 2-67 Mm.

Energy range of brightenings is $3×10^{18}$ to $5×10^{23}$ ergs.

Power-law index of energy distribution is approximately 1.7–1.8.

Abstract

Coronal loops on the east limb of the Sun were observed by SUMER on SOHO for several days. Small flare-like brightenings are detected very frequently in the hot flare line Fe~{\small XIX}. We find that the relatively intense events are in good coincidence with the transient brightenings seen by Yohkoh/SXT. A statistical analysis shows that these brightenings have durations of 5-84 min and extensions along the slit of 2-67 Mm. The integrated energy observed in Fe~{\small XIX} for each event is in the range of $3\times10^{18}-5\times10^{23}$ ergs, and the estimated thermal energy ranges from $10^{26}-10^{29}$ ergs. Application of the statistical method proposed by Parnell \& Jupp (2000) yields a value of 1.5 to 1.8 for the index of a power law relation between the frequency of the events and the radiated energy in Fe~{\small XIX}, and a value of 1.7 to 1.8 for the index of the frequency distribution of the thermal energy in the energy range $>10^{27}$ ergs. We examine the possibility that these small brightenings give a big contribution to heating of the active region corona.