Mapping the Magnetic Field of Flare Coronal Loops

The magnetic field is key to the dynamics, evolution, and heating of the solar atmosphere, yet direct measurements are rare and highly uncertain. We report on the unique observation of flaring coronal loops at the solar limb using high-resolution imaging spectropolarimetry from the Swedish 1-m Solar Telescope. The vantage position, orientation, and nature of the chromospheric material that filled the flare loops allowed us to determine their magnetic field with unprecedented accuracy using the weak-field approximation method. Our analysis reveals coronal magnetic field strengths as high as 350 G at heights up to 25 Mm above the solar limb. These measurements are substantially higher than a number of previous estimates and may have considerable implications for our current understanding of the extended solar atmosphere.