Microwave diagnostics of magnetic field strengths in solar flaring loops

TL;DR

This study uses microwave observations to map magnetic field strengths in solar flare loops, revealing a decrease from footpoints to higher altitudes, and demonstrates microwave imaging's potential in coronal magnetic diagnostics.

Contribution

First to utilize microwave imaging at two frequencies for detailed magnetic field mapping in solar flare loops, validating the method against magnetic modeling.

Findings

Magnetic field decreases from ~800 G at footpoints to ~100 G at higher altitudes.

Microwave imaging can effectively diagnose coronal magnetic fields with limited frequency data.

Results align with magnetic flux rope models.

Abstract

We have performed microwave diagnostics of the magnetic field strengths in solar flare loops based on the theory of gyrosynchrotron emission. From Nobeyama Radioheliograph observations of three flare events at 17 and 34 GHz, we obtained the degree of circular polarization and the spectral index of microwave flux density, which were then used to map the magnetic field strengths in post-flare loops. Our results show that the magnetic field strength typically decreases from ~800 G near the loop footpoints to ~100 G at a height of 10--25 Mm. Comparison of our results with magnetic field modeling using a flux rope insertion method is also discussed. Our study demonstrates the potential of microwave imaging observations, even at only two frequencies, in diagnosing the coronal magnetic field of flaring regions.