Dual Nature of M Dwarf Star: Auroral Activity Meets Solar-like Bursts

Our current understanding of astrophysical magnetic activity was historically grounded in observations within the solar system, where two separate magnetic activity regimes were first recognized. One is represented by auroral radio emission from magnetized planets, driven by electron cyclotron maser emission within large-scale, closed magnetospheres; the other is typified by the Sun, in which Type II/III radio bursts arise from coronal plasma emission along open magnetic field configurations. However, it remains unresolved whether these two distinct regimes, associated with divergent magnetic geometries, can operate on the same star, limited by both available diagnostic methods and coordinated multi-wavelength coverage. Here we report two sharply distinct forms of optical–radio association from the nearby M-dwarf binary G 9-38, uncovered through periodicity analysis combined with simultaneous radio, optical, and X-ray monitoring. One association arises from auroral activity, with both periodic radio pulses and optical brightening co-modulated on the stellar rotation period. The other association is characterised by the simultaneous occurrence of a fast-drifting, strongly polarized radio burst and an energetic optical flare, providing compelling evidence for a stellar analogue of a solar type III burst. Both forms of activity are localized to the same component, G 9-38A, implying that the auroral and flare-driven coherent radio emission mechanisms can coexist on an M dwarf. These results provide clear evidence that solar type III-like burst can operate within a strongly confined magnetosphere, bridging two traditionally separate regimes of magnetic activity from planets to the Sun.