Transient rotation of photospheric vector magnetic fields associated with a solar flare

TL;DR

This study reports a transient, reversible rotation of photospheric magnetic fields during a solar flare, observed with high-resolution imaging, suggesting untwisting of flare loops and involving high-energy processes.

Contribution

It presents the first high-resolution observation of transient magnetic field rotation during a solar flare, highlighting the dynamic untwisting of magnetic structures.

Findings

Transient azimuth angle change of 12°-20° during flare

Magnetic fields become more potential-like post-flare

High-energy electrons or Alfvén waves may drive the changes

Abstract

As one of the most violent eruptions on the Sun, flares are believed to be powered by magnetic reconnection. The fundamental physics involving the release, transfer and deposition of energy have been studied extensively. Taking advantage of the unprecedented resolution provided by the 1.6-m Goode Solar Telescope, here we show a sudden rotation of vector magnetic fields, about 12$^{\circ}$-20$^{\circ}$ counterclockwise, associated with a flare. Unlike the permanent changes reported previously, the azimuth-angle change is transient and co-spatial/temporal with H$\alpha$ emission. The measured azimuth angle becomes closer to that in potential fields suggesting untwist of flare loops. The magnetograms were obtained in the near infrared at 1.56~$\mu$m, which is minimally affected by flare emission and no intensity profile change was detected. We believe that these transient changes are real and discuss the possible explanations in which the high energy electron beams or $Alfv\acute{e}n$ waves play a crucial role.