Starspots as the origin of ultrafast drifting radio bursts from an active M dwarf
- Jiale Zhang
- Hui Tian
- Stefano Bellotti
- Tianqi Cang
- Joseph R. Callingham
- Harish K. Vedantham
- Bin Chen
- Sijie Yu
- Philippe Zarka
- Corentin K. Louis
- Peng Jiang
- Hongpeng Lu
- Yang Gao
- Jinghai Sun
- Hengqian Gan
- Hui Li
- Chun Sun
- Zheng Lei
- Menglin Huang
2025-10-17
Detecting coherent radio bursts from nearby M dwarfs provides opportunities for exploring their magnetic activity and interaction with orbiting exoplanets. However, it remains uncertain whether the emission is related to flare-like activity similar to the Sun or magnetospheric process akin to magnetized planets. Using observations (1.0 to 1.5 gigahertz) taken by the Five-hundred-meter Aperture Spherical radio Telescope, we found a type of millisecond-scale radio bursts with exceptionally high-frequency drift rates (~8 gigahertz per second) from an active M dwarf, AD Leo. The ultrafast drift rates point to a source region with a notably low magnetic scale height (<0.15 r ⋆ , r ⋆ as the stellar radius), a feature not expected in a commonly assumed dipole-like global field but highly possible in localized strong-field structures, i.e., starspots. Our findings suggest that a concentrated magnetic field above starspots could be responsible for some of the most intense radio bursts from M dwarfs, supporting a solar-like electron acceleration mechanism.