Accessing the fine temporal scale of EUV brightenings and their quasi-periodic pulsations: 1-second cadence observations by Solar Orbiter/EUI

¹ Solar-Terrestrial Centre of Excellence – SIDC, Royal Observatory of Belgium, Ringlaan -3- Av. Circulaire, 1180 Brussels, Belgium
² Centre for mathematical Plasma Astrophysics, Department of Mathematics, KU Leuven, Celestijnenlaan 200B, 3001 Leuven, Belgium
³ Astronomy & Astrophysics Section, School of Cosmic Physics, Dublin Institute for Advanced Studies, DIAS Dunsink Observatory, Dublin D15 XR2R, Ireland.
⁴ ETH-Zurich, Wolfgang-Pauli-Str. 27, 8093 Zurich, Switzerland
⁵ Physikalisch-Meteorologisches Observatorium Davos, World Radiation Center, 7260 Davos Dorf, Switzerland

^⋆ Corresponding author: daye.lim@oma.be

Received: 7 September 2025
Accepted: 6 October 2025

Abstract

Context. Small-scale extreme-ultraviolet (EUV) transient brightenings are observationally abundant and critically important to investigate. Determining whether they share the same physical mechanisms as larger-scale flares would have significant implications for the coronal heating problem. A recent study has revealed that quasi-periodic pulsations (QPPs), a common feature in both solar and stellar flares, could also be present in EUV brightenings in the quiet Sun (QS).

Aims. We aim to characterise the properties of EUV brightenings and their associated QPPs in both QS and active regions (ARs) using an unprecedented 1 s cadence observations from Solar Orbiter’s Extreme Ultraviolet Imager (Solar Orbiter/EUI).

Methods. We applied an automated detection algorithm to analyse statistical properties of EUV brightenings. The QPPs were identified using complementary techniques optimised for both stationary and non-stationary signals, including a Fourier-based method, ensemble empirical mode decomposition, and wavelet analysis.

Results. Over 500 000 and 300 000 brightenings were detected, respectively, in ARs and QS regions. Brightenings with lifetimes shorter than 3 s were detected, demonstrating the importance of high temporal resolution. The QPP occurrence rates were approximately 11% in AR brightenings and 9% in QS brightenings, with non-stationary QPPs being more common than stationary ones. The QPP periods range from 5 to over 500 s and display similar distributions between the ARs and QS regions. Moderate linear correlations were found between QPP periods and the lifetime and spatial scale of the associated brightenings, while no significant correlation was found with peak brightness. We found a consistent power-law scaling, with a weak correlation and a large spread, between QPP period and lifetime in EUV brightenings, solar, and stellar flares.

Conclusions. The results support the interpretation that EUV brightenings may represent a small-scale manifestation of the same physical mechanisms driving larger solar and stellar flares. Furthermore, the similarity in the statistical properties of EUV brightenings and their associated QPPs between ARs and QS regions suggests that the underlying generation mechanisms might not strongly depend on the large-scale magnetic environment.