Prof. Dale R. Gary
Department of Physics New Jersey Institute of Technology
Dynamic Measurement of Electron Acceleration and Coronal Magnetic Fields in Solar Flares
Solar flares are the result of explosive release of stored magnetic energy in the Sun's corona. The detailed physical processes that underlie the rapid conversion of such energy to other forms, particularly the acceleration of electrons and ions to relativistic energies, remain mysterious, partly because direct measurements of the coronal magnetic field and the spatial and energy distribution of the particles have been difficult or impossible. One emission mechanism that is sensitive to the coronal magnetic field in the flaring region is radio emission, but until now the instrument capabilities needed to exploit that sensitivity have not been available. However, within the past year this has changed with the completion of a new, solar dedicated radio interferometer array, the Expanded Owens Valley Solar Array (EOVSA), that has the required combination of spatial, spectral, and temporal resolution to make these breakthrough measurements. In this talk, I illustrate the new capabilities and their implications using observations of a showcase solar limb flare that occurred on 2017 September 10. This event is a textbook example of the "standard solar model" eruptive event, with a clearly visible reconnecting current sheet connecting an erupting flux rope with a growing arcade of newly formed "post-flare" loops. The comparison of microwave diagnostics of high-energy electrons with those from hard X-rays seen by the RHESSI spacecraft show that, while they are fully consistent, the microwaves reveal that the coronal volume containing high-energy particles is much larger and more widespread than would have been deduced from hard X-rays alone. Even more important, however, are the quantitative measurements of the spatially and temporally resolved magnetic field strength, which, if our interpretation is correct, directly reveal the conversion of magnetic energy over a large volume into high-energy charged particles.and turbulent plasma. The new observations present both a challenge and an opportunity for further theoretical understanding of the processes occurring in solar flares.