Investigation of white-light emission in circular-ribbon flares

TL;DR

This study statistically analyzes circular-ribbon solar flares, focusing on white-light emission, revealing correlations with flare energy and magnetic complexity across different flare classes.

Contribution

First comprehensive statistical investigation of white-light emission in circular-ribbon flares using SDO data from 2010 to 2017.

Findings

White-light flares occur in all X-class CFs and most M-class CFs.

White-light enhancement correlates with flare energy in X-class but not in M- and C-class.

CFs with white-light emission tend to have shorter duration, smaller size, and more complex magnetic fields.

Abstract

Using observations by the Solar Dynamics Observatory from June 2010 to December 2017, we have performed the first statistical investigation of circular-ribbon flares (CFs) and examined the white-light emission in these CFs. We find 90 CFs occurring in 36 active regions (ARs), including 8 X-class, 34 M-class, 48 C- and B-class flares. The occurrence rate of white-light flares (WLFs) is 100\% (8/8) for X-class CFs, $\sim$62\% (21/34) for M-class CFs, and $\sim$8\% (4/48) for C- and B-class CFs. Sometimes we observe several CFs in a single AR, and nearly all of them are WLFs. Compared to normal CFs, CFs with white-light enhancement tend to have a shorter duration, smaller size, stronger electric current and more complicated magnetic field. We find that for X-class WLFs, the white-light enhancement is positively correlated with the flare class, implying that the white-light enhancement is largely determined by the amount of released energy. However, there is no such correlation for M- and C-class WLFs, suggesting that other factors such as the time scale, spatial scale and magnetic field complexity may play important roles in the generation of white-light emission if the released energy is not high enough.