A Circular White-Light Flare with Impulsive and Gradual White-Light Kernels

TL;DR

This paper reports a rare nearly circular white-light flare with both impulsive and gradual kernels observed in detail, challenging existing models and suggesting multiple mechanisms for energy transport in the lower solar atmosphere.

Contribution

It presents detailed observations of a unique white-light flare with both impulsive and gradual kernels, highlighting the need for new models to explain the gradual kernels.

Findings

Presence of both impulsive and gradual white-light kernels in a single flare

Existing thick-target model explains impulsive kernels but not gradual ones

Multiple mechanisms like soft X-ray backwarming and Alfven waves may contribute

Abstract

White-light flares are the flares with emissions visible in the optical continuum. They are thought to be rare and pose the most stringent requirements in energy transport and heating in the lower atmosphere. Here we present a nearly circular white-light flare on 2015 March 10 that was well observed by the Optical and Near-infrared Solar Eruption Tracer and Solar Dynamics Observatory. In this flare, there appear simultaneously both impulsive and gradual white-light kernels. The generally accepted thick-target model would be responsible for the impulsive kernels but not sufficient to interpret the gradual kernels. Some other mechanisms including soft X-ray backwarming or downward-propagating Alfven waves, acting jointly with electron beam bombardment, provide a possible interpretation. However, the origin of this kind of white-light kernels is still an open question that induces more observations and researches in the future to decipher it.