Dynamic Microwave imaging Spectroscopy with the Expanded Owens Valley Solar Array
Dale Gary, New Jersey Institute of Technology
The Expanded Owens Valley Solar Array (EOVSA) has been operating since April 2017, obtaining multi-frequency images of flares and active regions in the microwave (2.5-18 GHz) frequency range at 1 s cadence. The resulting 4-D image cubes (two spatial, spectral, and temporal) provide the opportunity for true dynamic imaging spectroscopy. EOVSA observations of the 2017 September 10 X8.2 solar limb flare are used to illustrate the power of imaging spectroscopy in this frequency range for studying the details of magnetic reconnection, energy release, particle acceleration, and transport over the entire duration of the event. For the first time, we are able to measure the dynamic changes in coronal magnetic field and its associated energy density as a function of position in the flaring region. The simultaneous microwave diagnostics of high-energy electrons additionally allows us to "follow the energy" and relate magnetic energy release to acceleration of particles. In the later phase of the flare, the emission is dominated by superhot thermal plasma, modulated by episodic particle acceleration from collapsing loops. EOVSA's 7-day-per-week, full-Sun coverage of solar flares since April 2017, and during the upcoming solar cycle 25, is producing a fantastic new, open data source for the world-wide solar community. We encourage the community of European solar radio astronomers to help us build the tools and techniques for exploiting this rich data set.