Starspots as the origin of ultrafast drifting radio bursts from an active M dwarf

TL;DR

This study reports ultrafast drifting radio bursts from an active M dwarf, likely originating from starspot-associated magnetic structures, revealing insights into stellar magnetic activity and electron acceleration mechanisms.

Contribution

It demonstrates that localized strong magnetic fields above starspots can produce intense, ultrafast drifting radio bursts, a novel explanation for such phenomena in M dwarfs.

Findings

Detected millisecond-scale radio bursts with high drift rates from AD Leo

Low magnetic scale height suggests origin in starspot magnetic structures

Supports solar-like electron acceleration mechanisms in stellar environments

Abstract

Detecting coherent radio bursts from nearby M dwarfs provides opportunities for exploring their magnetic activity and interaction with orbiting exoplanets. However, it remains uncertain if the emission is related to flare-like activity similar to the Sun or magnetospheric process akin to magnetized planets. Using observations (1.0 - 1.5 GHz) 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 ($\sim 8\;\rm{GHz\;s^{-1}}$) from an active M dwarf, AD Leo. The ultrafast drift rates point to a source region with a notably low magnetic scale height ($<0.15\; r_\star$, $r_\star$ 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.