Flare Ribbons Observed with G-band and FeI 6302A Filters of the Solar Optical Telescope on Board Hinode

TL;DR

This study used high-resolution images from Hinode's Solar Optical Telescope to analyze the fine structures of flare ribbons in multiple wavelengths, revealing new details about their morphology, heating mechanisms, and magnetic transient phenomena.

Contribution

First high-resolution observation of flare ribbons in G-band and FeI 6302A lines, revealing fine structures and insights into heating and magnetic transient effects.

Findings

Flare ribbons show sharp leading edges and diffuse interiors in G-band.

Diffuse emission depth estimated at about 100 km or less.

Transient polarity reversal observed in FeI 6302A during flare.

Abstract

The Solar Optical Telescope (SOT) on board Hinode satellite observed an X3.4 class flare on 2006 December 13. Typical two-ribbon structure was observed, not only in the chromospheric CaII H line but also in G-band and FeI 6302A line. The high-resolution, seeing-free images achieved by SOT revealed, for the first time, the sub-arcsec fine structures of the "white light" flare. The G-band flare ribbons on sunspot umbrae showed a sharp leading edge followed by a diffuse inside, as well as previously known core-halo structure. The underlying structures such as umbral dots, penumbral filaments and granules were visible in the flare ribbons. Assuming that the sharp leading edge was directly heated by particle beam and the diffuse parts were heated by radiative back-warming, we estimate the depth of the diffuse flare emission using the intensity profile of the flare ribbon. We found that the depth of the diffuse emission is about 100 km or less from the height of the source of radiative back-warming. The flare ribbons were also visible in the Stokes-V images of FeI 6302A, as a transient polarity reversal. This is probably related to "magnetic transient" reported in the literature. The intensity increase in Stokes-I images indicates that the FeI 6302A line was significantly deformed by the flare, which may cause such a magnetic transient.