Fine-scale flare structures and their energetic implications from short-exposure extreme-ultraviolet imaging
5 affiliations
- 1Astronomy & Astrophysics Section, Dublin Institute for Advanced Studies
- 2University of Applied Sciences and Arts Northwestern Switzerland
- 3University College London, Mullard Space Science Laboratory
- 4Solar-Terrestrial Centre of Excellence – SIDC, Royal Observatory of Belgium
- 5Solar Physics Laboratory, Heliophysics Science Division, NASA Goddard Space Flight Center
Abstract
Context. To capture the brightest and most rapidly evolving phases of solar flares, the Major Flare Solar Orbiter Observing Plan (SOOP) employs a dedicated short-exposure mode for the High Resolution Imager (HRIEUV) of the Extreme Ultraviolet Imager (EUI), providing high-cadence, high spatial-resolution extreme-ultraviolet (EUV) imaging. Aims. We investigated the spatial and temporal organisation of compact flare emission and its implications for local energy deposition, using high-cadence, short-exposure HRIEUV observations of the 2024 March 19 M2.1 flare. Methods. We combined the short-exposure (0.04 s) HRIEUV observations with hard X-ray (HXR) timing, imaging, and spectroscopic data from the Spectrometer Telescope for Imaging X-rays (STIX). We characterised impulsive ribbon kernels and later loop strands and compared footpoint areas measured with HRIEUV, the Atmospheric Imaging Assembly (AIA), and STIX to constrain the local energy flux carried by flare-accelerated electrons. Results. The short-exposure observations reveal compact flare emission largely obscured by saturation in normal-exposure HRIEUV and AIA imaging. The spatially integrated HRIEUV emission evolves co-temporally with the STIX 22–45 keV HXR emission, with no lag discernible beyond the 2 s HRIEUV sampling. The ribbons comprise repeatedly activated kernels with characteristic separations of ∼1.4–1.7 Mm, while the developing arcade shows a similar strand separation of ∼1.3 Mm. This result indicates that this ∼1–2 Mm spatial organisation persists into the newly formed flare loops. Measured kernel and strand widths of ∼0.4–0.5 Mm lie close to the instrumental resolution limit. The compact HRIEUV footpoint areas are approximately an order of magnitude smaller than those inferred from AIA or STIX, implying nominal, local non-thermal energy fluxes of the order of 1011 erg cm−2 s−1 at the HXR peaks. These estimates remain substantially higher across the tested intensity thresholds, although their absolute values depend on the area definition and spectral modelling Conclusions. The combination of high dynamic range, high spatial resolution, and high cadence in the HRIEUV short-exposure observations reveals a characteristic spatial organisation of the flare emission on scales of ∼1–2 Mm, as well as substantially higher local non-thermal energy fluxes than inferred from conventional EUV or HXR source areas. These results demonstrate the value of flare-optimised EUV imaging for future solar flare observations.
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BibTeX
@article{laura2026finescale,
title = {{Fine-scale flare structures and their energetic implications from short-exposure extreme-ultraviolet imaging}},
author = {Hayes Laura A. and Collier Hannah and Krucker Säm and Ryan Daniel and Berghmans David and Kraaikamp Emil and Stiefel Muriel and Inglis Andrew},
journal = {Astronomy \& Astrophysics},
year = {2026},
month = oct,
doi = {10.1051/0004-6361/202662625},
url = {https://doi.org/10.1051/0004-6361/202662625},
note = {CC BY},
}
RIS
TY - JOUR
TI - Fine-scale flare structures and their energetic implications from short-exposure extreme-ultraviolet imaging
AU - Hayes Laura A.
AU - Collier Hannah
AU - Krucker Säm
AU - Ryan Daniel
AU - Berghmans David
AU - Kraaikamp Emil
AU - Stiefel Muriel
AU - Inglis Andrew
PY - 2026
DA - 2026/10/24
JO - Astronomy & Astrophysics
DO - 10.1051/0004-6361/202662625
UR - https://doi.org/10.1051/0004-6361/202662625
AB - Context. To capture the brightest and most rapidly evolving phases of solar flares, the Major Flare Solar Orbiter Observing Plan (SOOP) employs a dedicated short-exposure mode for the High Resolution Imager (HRIEUV) of the Extreme Ultraviolet Imager (EUI), providing high-cadence, high spatial-resolution extreme-ultraviolet (EUV) imaging. Aims. We investigated the spatial and temporal organisation of compact flare emission and its implications for local energy deposition, using high-cadence, short-exposure HRIEUV observations of the 2024 March 19 M2.1 flare. Methods. We combined the short-exposure (0.04 s) HRIEUV observations with hard X-ray (HXR) timing, imaging, and spectroscopic data from the Spectrometer Telescope for Imaging X-rays (STIX). We characterised impulsive ribbon kernels and later loop strands and compared footpoint areas measured with HRIEUV, the Atmospheric Imaging Assembly (AIA), and STIX to constrain the local energy flux carried by flare-accelerated electrons. Results. The short-exposure observations reveal compact flare emission largely obscured by saturation in normal-exposure HRIEUV and AIA imaging. The spatially integrated HRIEUV emission evolves co-temporally with the STIX 22–45 keV HXR emission, with no lag discernible beyond the 2 s HRIEUV sampling. The ribbons comprise repeatedly activated kernels with characteristic separations of ∼1.4–1.7 Mm, while the developing arcade shows a similar strand separation of ∼1.3 Mm. This result indicates that this ∼1–2 Mm spatial organisation persists into the newly formed flare loops. Measured kernel and strand widths of ∼0.4–0.5 Mm lie close to the instrumental resolution limit. The compact HRIEUV footpoint areas are approximately an order of magnitude smaller than those inferred from AIA or STIX, implying nominal, local non-thermal energy fluxes of the order of 1011 erg cm−2 s−1 at the HXR peaks. These estimates remain substantially higher across the tested intensity thresholds, although their absolute values depend on the area definition and spectral modelling Conclusions. The combination of high dynamic range, high spatial resolution, and high cadence in the HRIEUV short-exposure observations reveals a characteristic spatial organisation of the flare emission on scales of ∼1–2 Mm, as well as substantially higher local non-thermal energy fluxes than inferred from conventional EUV or HXR source areas. These results demonstrate the value of flare-optimised EUV imaging for future solar flare observations.
SN - 0004-6361
SN - 1432-0746
ER -