Figure 1: Interface of the GSFIT widget with a selected EOVSA image (left panel) at 8.71 GHz of a large 2022-Oct-02 solar flare. Middle panel shows a spatially resolved spectrum (white symbols with uncertainties) from the location shown by intersection of vertical and horizontal dashed red lines in the left panel. The green line is the model spectral fit to the data. The fit parameters with their uncertainties are printed in this panel in yellow. The right panel shows the input parameters for the fitting.

The project is funded by the German Science Foundation (DFG) for a period of three years to support one postdoc FTE, currently - Dr Tatiana Kaltman, and aims at improving our ability to measure and model coronal magnetic field and study associated phenomena. The project will obtain new fundamental knowledge on magnetic reconnection and particle acceleration in solar flares via (i) measuring the coronal magnetic field and its variations; (ii) measuring the nonthermal electron distributions and evaluating a typical efficiency of acceleration; and (iii) understanding these dynamics in the 3D domain. The project will combine the remote sensing of the evolving coronal magnetic field and other parameters in solar flares with data-constrained 3D modeling. The project will yield evolving microwave images of solar flares and active regions, evolving maps of coronal parameters such as magnetic field (see Figure) and plasma densities, new physical phenomena derived from these data and data products, and 3D models of these phenomena.

Figure 2: Maps (44′′ × 44′′) of the coronal magnetic field strength and thermal electron number density, along with their standard deviations inferred over the one-minute interval 18:57:00–18:58:00 UT. The red contour shows the 20% ROI level from Hinode/XRT at 18:56:24.9 UT, and the violet contour indicates the 10% brightness level from the 5.79 GHz EOVSA image at 18:55:44 UT.

Within this project, we, in particular, analyze the 2021-May-07 solar flare (see, e.g., Ryan et al. 2024; Mondal et al. 2024) using microwave EOVSA observations to recover the magnetic field values in the SXR source studied stereoscopically by Ryan et al. (2024). The 3D geometry derived from stereoscopic X-ray data is then used to reconstruct the spatial structure of the magnetic field, Alfvén velocity, and plasma beta in the flaring region. Figure 2 shows regularized maps of the coronal magnetic field strength and thermal electron number density with their uncertainties. These maps clearly demonstrate a nice thermal loop with the electron number density that closely matches that thermal number density inferred from the soft X-ray analysis. This permits us to associate the main source with the SXR source and assign 3D coordinates of the SXR source reported by Ryan et al. (2024) to the microwave-inferred magnetic field values. The reconstructed 3D maps of magnetic field strength and plasma number density allow us to derive key physical parameters that govern plasma dynamics in the solar corona, most notably the Alfvén speed and the plasma beta; see Figure 3.