Extent of solar-like spectral peak variability in M-dwarf radio flares

Determine the extent to which the solar phenomenon of variable gyrosynchrotron spectral peak frequencies (commonly 5–10 GHz but sometimes up to 37 GHz) is replicated in M-dwarf flares by measuring and characterizing the spectral peak locations and their evolution during AU Mic and other M-dwarf flares in the 5–37 GHz range, including assessment of optically thick emission at higher frequencies.

Background

In solar flares, the gyrosynchrotron spectrum often peaks between 5–10 GHz, but peaks up to 37 GHz have been observed. The paper notes that these frequencies are largely unobserved in M-dwarf flares, leaving uncertainty about whether similar behavior occurs in M-dwarf systems.

The authors’ Ku/K band observations (12–27 GHz) probe a regime where spectral peaks could lie within or above the observed bands. Establishing whether solar-like peak variability occurs in M dwarfs would clarify flare energetics, source sizes, and electron densities at high radio frequencies.

References

As these frequencies are largely unobserved in M-dwarf flares, the extent to which this solar phenomenon is replicated in M-dwarf flares is unknown \citep{White2011, Gary2023}.

— A 7-Day Multi-Wavelength Flare Campaign on AU Mic. II: Electron Densities and Kinetic Energies from High-Frequency Radio Flares  (2503.14624 - Tristan et al., 18 Mar 2025) in Section 1 (Introduction)

The more intense Ku-band flare is optically thick during the rise and peak, though the evolution beyond that is obscured (Figure~\ref{fig:flares}). This is consistent with many other small to moderate Ku-band flares from AU Mic, and the average radio $\nu_{\text{peak}$ in M-dwarf flares is currently unknown.

— Broadband 12-26 GHz Radio Radiation Reveals Evidence for Micro-flares on AU Mic  (2608.25400 - Tristan et al., 26 Aug 2026) in Section 5.2, Discussion, subsection “Flare Considerations”