Presentation #124.10 in the session High-Energy Solar Investigations Through Next-Generation Remote Sensing: Spectroscopy, Imaging, and Beyond — Poster Session.
Solar flares are powered by a rapid release of energy in the solar corona, thought to be produced by the decay of the coronal magnetic field strength. Direct quantitative measurements of the evolving magnetic field strength are required to test this. We report microwave observations of a solar flare, showing spatial and temporal changes in the coronal magnetic field (Fleishman et al. Science, 2020). The field decays at a rate of ~5 Gauss per second for 2 minutes, as measured within a flare subvolume of ~1028 cubic centimeters. The decrease in stored magnetic energy is enough to power the solar flare, including the associated eruption, particle acceleration, and plasma heating. This fast rate of decay implies a sufficiently strong electric field to account for the particle acceleration that produces the microwave emission. We report evolving spatially resolved distributions of thermal and nonthermal electrons in a solar flare derived from the same set of microwave observations (Fleishman et al. Nature, 2022) that unveil the true extent of the acceleration region compared with X-ray observations. Indeed, hard X-rays, produced by high-energy electrons accelerated in the flare, require a high ambient density for their detection that restricts the observed volume to denser regions that do not necessarily sample the entire volume of accelerated electrons. The distributions reported here reveal a volume filled with only (or almost only) nonthermal electrons, while being depleted of the thermal plasma, indicating that all electrons have experienced a prominent acceleration there. This volume is isolated from a surrounding, more typical flare plasma of mainly thermal particles with a smaller proportion of nonthermal electrons. This highly efficient acceleration happens in the same volume where the free magnetic energy is being released.