High Resolution Observations of the Low Atmospheric Response to Small Coronal Heating Events in an Active Region Core

TL;DR

This study uses high-resolution spectral observations from IRIS and SST to analyze small-scale coronal heating events, revealing the role of non-thermal electrons and thermal conduction in low atmospheric heating.

Contribution

First coordinated high-resolution observations of chromospheric response to coronal heating events, combined with machine learning and modeling, to understand heating mechanisms.

Findings

Chromospheric brightenings down to ~150km observed.

Coherence in spectral properties suggests coherent heating distribution.

Both non-thermal electrons and thermal conduction contribute to heating.

Abstract

High resolution spectral observations of the lower solar atmosphere (chromosphere and transition region) during coronal heating events, in combination with predictions from models of impulsively heated loops, provide powerful diagnostics of the properties of the heating in active region cores. Here we analyze the first coordinated observations of such events with the Interface Region Imaging Spectrograph (IRIS) and the CHROMospheric Imaging Spectrometer (CHROMIS), at the Swedish 1-m Solar Telescope (SST), which provided extremely high spatial resolution and revealed chromospheric brightenings with spatial dimensions down to ~150km. We use machine learning methods (k-means clustering) and find significant coherence in the spatial and temporal properties of the chromospheric spectra, suggesting, in turn, coherence in the spatial and temporal distribution of the coronal heating. The comparison of IRIS and CHROMIS spectra with simulations suggest that both non-thermal electrons with low energy (low-energy cutoff ~5keV) and direct heating in the corona transported by thermal conduction contribute to the heating of the low atmosphere. This is consistent with growing evidence that non-thermal electrons are not uncommon in small heating events (nano- to micro-flares), and that their properties can be constrained by chromospheric and transition region spectral observations.