Enhancing the detection of low-energy M dwarf flares: wavelet-based denoising of CHEOPS data

Abstract

Stellar flares are powerful bursts of electromagnetic radiation triggered by magnetic reconnection in the chromosphere of stars, occurring frequently and intensely on active M dwarfs. While missions like TESS and Kepler have studied regular and super-flares, their detection of flares with energies below 10^30 erg remains incomplete. Extending flare studies to include these low-energy events could enhance flare formation models and provide insight into their impacts on exoplanetary atmospheres. This study investigates CHEOPS's capacity to detect low-energy flares in M dwarf light curves. Using CHEOPS's high photometric precision and observing cadence, along with a tailored wavelet-based denoising algorithm, we aim to improve detection completeness and refine flare statistics for low-energy events. We conducted a flare injection and recovery process to optimise denoising parameters, applied it to CHEOPS light curves to maximise detection rates, and used a flare breakdown algorithm to analyse complex structures. Our analysis recovered 349 flares with energies ranging from 2.2×10^26 to 8.1×10^30 erg across 63 M dwarfs, with ∼40% exhibiting complex, multi-peaked structures. The denoising algorithm improved flare recovery by ∼34%, though it marginally extended the lower boundary of detectable energies. For the full sample, the power-law index α was 1.92±0.07, but a log-normal distribution fit better, suggesting multiple flare formation scenarios. While CHEOPS's observing mode is not ideal for large-scale surveys, it captures weaker flares than TESS or Kepler, expanding the observed energy range. Wavelet-based denoising enhances low-energy event recovery, enabling exploration of the micro-flaring regime. Expanding low-energy flare observations could refine flare generation models and improve the understanding of their role in star-planet interactions.