We discuss acceleration and transport of electrons in the circular flare SOL2024-03-25T06:37:00 of the M4.4 X-ray class, characterized by a record-short duration of hard X-ray emission pulse. We have used radio data in the 0.1–40 GHz range, including images of the flare region in the Siberian Radio Heliograph frequency range. Microwave and hard X-ray emissions are generated in the vicinity of the magnetic domain by the interaction of ropes visible at 1600 Å. The impulsive stage ended with a short peak <5 s long, recorded simultaneously at 35 GHz and in the 100–300 keV range. After the peak under ropes, a long loop in the ultraviolet (UV) rises and a broad plasma ejection appears which is directed along the outer spine observed before the flare. Large loops connect the spine and the remote source. There is a broadband microwave source at the remote footpoint at 215 arc. sec., with the delay of its maximum from the peak in the flare core being ~5 s, and the electron propagation velocity along the large loops estimated at one-third of the velocity of light. A distinctive feature of the radiation of the remote source was high degree of its circular polarization. The meter flare emission indicates that tops of large loops are filled with non-thermal electrons with large pitch angles. The set of spatial, spectral, and polarization characteristics of microwave sources obtained for the first time is discussed in the context of the known results on the nature of circular ribbon flares.
Altyntsev et al. (2025) studied this question.