Radio Constraints on Particle Acceleration in Micro and Multiwavelength Flares on AU Mic

Stellar flares on M-dwarfs are more energetic and frequent than their solar counterparts. While these events impact exoplanet habitability, few multiwavelength campaigns exist to constrain their underlying particle acceleration physics. We present high-frequency Karl G. Jansky Very Large Array (JVLA) radio data from two multiwavelength campaigns targeting AU Mic, a 22 Myr active M-dwarf hosting a debris disk and transiting exoplanets. Radio observations uniquely probe gyrosynchrotron radiation from accelerated electrons within magnetic loops. Specifically, constraining the optically thin spectral index informs the electron energy distribution, which is a major outstanding parameter in broadband stellar flare modeling. The first campaign includes 20 hours of 12–18 GHz data over four days, where 25% of detected flares are optically thin. For these events, the total electron kinetic energy can explain the simultaneous, multiwavelength radiated energy if magnetic field strengths are within 500–700 G. Furthermore, the quiescent baseline (1–3 mJy) exhibits a variable, optically thin gyrosynchrotron component with spectral indices similar to some flares. This persistent emission likely arises from continuous particle acceleration from unresolved micro-flares across the stellar surface. The second campaign comprises 5 hours of sequential 12–18 GHz and 18–26 GHz observations. The quiescent flux is fainter (~0.4 mJy) but is best described by a gyrosynchrotron spectrum peaking at ~17 GHz. This spectral shape suggests compact source regions (<1% of the stellar surface) with strong ~1 kG magnetic fields, further supporting micro-flaring. These campaigns suggest that continuous micro-flaring drives the high-frequency, non-thermal radio environment of active M-dwarfs, though further multiwavelength flare relations and their impacts on space weather will require dedicated follow-up observations.