Chromospheric emission from nanoflare heating in RADYN simulations

TL;DR

This study uses RADYN simulations to analyze how nanoflare-driven non-thermal electrons influence chromospheric spectral lines, providing insights into detecting small-scale heating events in the solar atmosphere.

Contribution

It introduces a detailed analysis of spectral line formation under nanoflare conditions, highlighting the diagnostic potential of chromospheric emissions for small-scale solar heating events.

Findings

Spectral signatures depend on loop density and electron cutoff energy.

Low-energy electrons cause plasma flows leading to spectral shifts.

Higher-energy electrons increase local chromospheric emission.

Abstract

Heating signatures from small-scale magnetic reconnection events in the solar atmosphere have proven to be difficult to detect through observations. Numerical models that reproduce flaring conditions are essential in the understanding of how nanoflares may act as a heating mechanism of the corona. We study the effects of non-thermal electrons in synthetic spectra from 1D hydrodynamic RADYN simulations of nanoflare heated loops to investigate the diagnostic potential of chromospheric emission from small-scale events. The Mg II h and k, Ca II H and K, Ca II 854.2 nm, H-alpha and H-beta chromospheric lines were synthesised from various RADYN models of coronal loops subject to electron beams of nanoflare energies. The contribution function to the line intensity was computed to better understand how the atmospheric response to the non-thermal electrons affects the formation of spectral lines and the detailed shape of their spectral profiles. The spectral line signatures arising from the electron beams highly depend on the density of the loop and the lower cutoff energy of the electrons. Low-energy (5 keV) electrons deposit their energy in the corona and transition region, producing strong plasma flows that cause both redshifts and blueshifts of the chromospheric spectra. Higher-energy (10 and 15 keV) electrons deposit their energy in the lower transition region and chromosphere, resulting in increased emission from local heating. Our results indicate that effects from small-scale events can be observed with ground-based telescopes, expanding the list of possible diagnostics for the presence and properties of nanoflares.