Optical Continuum Light Curves and Bolometric Energy Estimates of Solar White-light Flares

TL;DR

The study tackles the limited availability of optical continuum light curves for solar white-light flares by assembling a dataset of $70$ events from SDO/HMI and SDO/AIA, covering flare classes from $C$ to $X$. It introduces a robust end-to-end pipeline—comprising limb-darkening and solar-rotation corrections, ribbon-based WL signal identification, and careful detrending—to extract high-quality light curves and derive bolometric energies and durations. Bolometric energetics are computed with two approaches: a conventional fixed-temperature model with $T_{ m flare}=10^{4} m\,K$ and a refined variable-temperature method that accounts for spatially varying backgrounds, revealing a mean energy ratio $E_2/E_1\approx0.23$ and highlighting substantial overestimation by the fixed-temperature method. The authors release a comprehensive dataset (three data products per event) to support statistical analyses and solar–stellar flare comparisons, and they plan to scale the methodology to the full SDO dataset to build a larger solar WLF catalog.

Abstract

Solar white-light flares (WLFs) are solar flares exhibiting enhanced emission in the optical continuum. They are critical for understanding energy release and transport mechanisms in solar flares and for conducting comparative studies with stellar WLFs. However, the scarcity of accurately and reliably measured optical continuum light curves for solar WLFs significantly hampers related studies. Based on the optimized solar WLF identification method, we construct a dataset of optical continuum light curves for 70 solar WLFs using 6173 Å continuum intensity images from the Solar Dynamics Observatory. Moreover, for each solar WLF event, we also provide the location of the white-light emission enhancement signals and key parameters including bolometric energies and durations derived from both the traditional fixed-temperature blackbody model and the refined variable-temperature blackbody model. This dataset will serve as a valuable resource for future statistical investigations of solar WLFs and for comparative studies between solar and stellar flares.

Figures (6)

• Figure 1: Demonstration of limb-darkening correction for SDO/HMI 6173 Å continuum intensity images. (a) Original solar continuum intensity image observed by SDO/HMI at 04:22:30 UT on 09 May 2024. (b) The corresponding image after the limb-darkening correction has been applied.
• Figure 2: Demonstration of solar rotation correction on SDO/HMI 6173 Å continuum intensity images. (a) Original solar continuum intensity image observed by SDO/HMI at 04:22:30 UT on 09 May 2024. (b) The corresponding image after being differentially rotated to a common reference time of 02:57:45 UT on the same day. The red circles in both panels highlight the same feature region.
• Figure 3: Spatial distributions of WL emission enhancement signals within flare ribbon regions for four representative solar WLFs. (a)-(d): SDO/HMI 6173 Å continuum intensity images for an X1.3-class solar WLFs on 2012 March 7, a C8.3-class solar WLFs on 2012 July 5, an M2.8-class solar WLFs on 2024 May 2, and an M2.2-class solar WLFs on 2024 May 10, respectively. In each panel, the flare ribbon regions, as identified from SDO/AIA 1600 Å observations, are outlined in red. The detected WL emission enhancement signals (WLF signals) within these flare ribbon regions are highlighted by the blue patches.
• Figure 4: Data processing pipeline for extracting solar WLF parameters from a SDO/HMI 6173 Å continuum light curve. (a) The original optical continuum light curve (blue solid line) with its baseline (orange dashed line) derived by a iterative sigma-clipping method. (b) The background-subtracted optical continuum light curve obtained by removing the baseline from the original data. (c) The interpolated optical continuum light curve used for precise measurement of bolometric energy and duration for each solar WLF. The vertical dashed lines mark the start, peak, and end times of the solar WLF, determined using the e-folding method.
• Figure 5: Comparison of bolometric energies derived from the two calculation methods. (a) Distributions of bolometric energies for solar WLFs calculated using the fixed-temperature blackbody model and the refined variable-temperature blackbody model. (b) Distribution of the ratio between the two bolometric energies ($E_2 / E_1$).