The White-light Emissions in Two X-class Flares Observed by ASO-S and CHASE

Abstract

The white-light continuum emissions in solar flares (i.e., white-light flares) are usually observed on the solar disk but, in a few cases, off the limb. Here we present on-disk as well as off-limb continuum emissions at 3600 Å (in the Balmer continuum) in an X2.1 flare (SOL2023-03-03T17:52) and an X1.5 flare (SOL2023-08-07T20:46), respectively, observed by the White-light Solar Telescope on the Advanced Space-based Solar Observatory. These continuum emissions are seen at the ribbons for the X2.1 flare and on loops during the X1.5 event, in which the latter also appears in the decay phase. These emissions also show up in the pseudocontinuum images at Fe i λ6173 from the Helioseismic and Magnetic Imager on the Solar Dynamics Observatory. In addition, the ribbon sources in the X2.1 flare exhibit significant enhancements in the Fe i line at 6569.2 Å and the nearby continuum observed by the Chinese Hα Solar Explorer. It is found that the on-disk continuum emissions in the X2.1 flare are related to a nonthermal electron-beam heating either directly or indirectly, while the off-limb emissions in the X1.5 flare are associated with thermal plasma cooling or due to Thomson scattering. These comprehensive continuum observations provide good constraints on flare energy deposition models, which helps us to better understand the physical mechanism of white-light flares.