Observing coronal nanoflares in active region moss

TL;DR

High-resolution Hi-C images reveal rapid, small-scale variability in moss regions, indicating that coronal nanoflares associated with magnetic reconnection likely contribute to coronal heating, challenging previous steady-heating assumptions.

Contribution

This study provides the first high-resolution observations of rapid moss variability, linking it to nanoflare heating events in the solar corona.

Findings

Detected variability on ~15s timescales in moss regions.

Linked moss variability to dynamic hot coronal loops and reconnection.

Estimated nanoflare energies to be at least a few 10^{23} erg.

Abstract

The High-resolution Coronal Imager (Hi-C) has provided Fe XII 193A images of the upper transition region moss at an unprecedented spatial (~0.3-0.4 arcsec) and temporal (5.5s) resolution. The Hi-C observations show in some moss regions variability on timescales down to ~15s, significantly shorter than the minute scale variability typically found in previous observations of moss, therefore challenging the conclusion of moss being heated in a mostly steady manner. These rapid variability moss regions are located at the footpoints of bright hot coronal loops observed by SDO/AIA in the 94A channel, and by Hinode/XRT. The configuration of these loops is highly dynamic, and suggestive of slipping reconnection. We interpret these events as signatures of heating events associated with reconnection occurring in the overlying hot coronal loops, i.e., coronal nanoflares. We estimate the order of magnitude of the energy in these events to be of at least a few $10^{23}rg, also supporting the nanoflare scenario. These Hi-C observations suggest that future observations at comparable high spatial and temporal resolution, with more extensive temperature coverage are required to determine the exact characteristics of the heating mechanism(s).