Bright millimeter flares from M dwarfs in CMB Experiments

Recently, the South Pole Telescope and the Atacama Cosmology Telescope reported the detection of several bright stellar transients in millimeter wavelengths. Five of these events are from rapidly rotating young M dwarfs. The luminosity of these events reaches 10^29 erg/s, which is 5 orders of magnitude greater than the largest solar flares in
millimeters and 4 orders of magnitude greater than the millimeter flares observed from Proxima Cen and AU Mic. These flares are also unusual due to their flat to rising spectra. We discuss plausible emission mechanisms for these events as well as parameters for the underlying energetic electron and proton flux. These events offer a glimpse into the extreme energetic particle environment surrounding young M dwarfs and the evolution of planetary atmospheres around them.