Spectral Observations and Modeling of a Solar White-light Flare Observed by CHASE

Abstract

The heating mechanisms of solar white-light flares remain unclear. We present an X1.0 white-light flare on 2022 October 2 (SOL2022-10-02T20:25) observed by the Chinese Hα Solar Explorer that provides two-dimensional spectra in the visible light for the full solar disk with a seeing-free condition. The flare shows a prominent enhancement of ∼40% in the photospheric Fe i line at 6569.2 Å, and the nearby continuum also exhibits a maximum enhancement of ∼40%. For the continuum near the Fe i line at 6173 Å from the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory, it is enhanced up to ∼20%. At the white-light kernels, the Fe i line at 6569.2 Å has a symmetric Gaussian profile that is still in absorption and the Hα line at 6562.8 Å displays a very broad emission profile with a central reversal plus a red or blue asymmetry. The white-light kernels are cospatial with the microwave footpoint sources observed by the Expanded Owens Valley Solar Array and the time profile of the white-light emission matches that of the hard X-ray emission above 30 keV from the Gamma-ray Burst Monitor (GBM) on Fermi. These facts indicate that the white-light emission is qualitatively related to a nonthermal electron beam. We also perform a radiative hydrodynamic simulation with the electron-beam parameters constrained by the hard X-ray observations from Fermi/GBM. The result reveals that the white-light enhancement cannot be well explained by a pure electron-beam heating together with its induced radiative backwarming but may need additional heating sources such as Alfvén waves.

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

“…The differences between the two flares are mainly from the values of white-light enhancements and the degree of asymmetry in the Hα line. The X2.1 flare in this study has much larger enhancements (>60%) in the HMI and CHASE continua than the X1.0 flare (40%) in Song et al (2023). For the line asymmetry, Hα shows a weak asymmetry in the X2.1 flare, whereas in the X1.0 flare it exhibits an obvious asymmetry.…”

“…It is interesting to compare the on-disk X2.1 WLF under study with the X1.0 WLF studied by Song et al (2023). These two flares share similarities but have differences too.…”

“…For the heating mechanisms, there have been proposed four types: (1) beams of electrons (Hudson 1972;Fletcher et al 2007;Krucker et al 2015) and protons (Machado et al 1978;Procházka et al 2018), (2) irradiation from X-rays (e.g., Henoux & Nakagawa 1977) or EUV (e.g., Poland et al 1988) and radiative back-warming from chromosphere (e.g., Ding et al 2003;Xu et al 2004), (3) chromospheric condensation (Gan et al 1992;Kowalski et al 2015), and (4) Alfvén waves (Emslie & Sturrock 1982;Fletcher & Hudson 2008). Note that in a certain flare, multiple mechanisms could play roles in producing the white-light emission (e.g., Machado et al 1978;Xu et al 2006;Hao et al 2017;Song et al 2023).…”

Simultaneous Horizontal and Vertical Oscillation of a Quiescent Filament Observed by CHASE and SDO

“…On 2022 October 2, an X1.0 flare occurred in the active region (AR) 13110 and 13113, which was accompanied by an EUV wave (Moreton wave) and a non-radial CME. The heating mechanisms related to the flare have been reported by Song et al (2023). In this paper, based on the imaging and spectroscopic observations, we focus on the simultaneous POS horizontal oscillation and winking phenomenon of a quiescent filament triggered by the EUV wave and Moreton wave, which was rarely reported in previous studies.…”