The Lyman-alpha Emission in Solar Flares. II. A Statistical Study on Its Relationship with the White-light plus Soft X-ray Emission

TL;DR

This study statistically analyzes 69 solar white-light flares to explore the relationships among Lyman-alpha, soft X-ray, and white-light emissions, revealing correlations in timing, energy, and rise times that inform models of energy transport in solar flares.

Contribution

It provides the first comprehensive statistical analysis of the relationships among ext{Ly} ext{ extalpha}, SXR, and WL emissions in solar flares, offering new constraints for energy transport models.

Findings

Positive power-law relationships among peak enhancements in SXR, ext{Ly} ext{ extalpha}, and WL.

ext{Ly} ext{ extalpha} peak is nearly co-temporal with SXR derivative peak.

Radiated energies in ext{Ly} ext{ extalpha} and WL are proportional to flare duration.

Abstract

The hydrogen \lya\ line and the white-light (WL) continuum are two key diagnostics of energy transport in the lower atmosphere during solar flares, yet their relationship remains poorly understood. Here we present a statistical analysis of 69 white-light flares (WLFs) to investigate the relationships among the \lya, soft X-ray (SXR), and WL continuum emissions using the data from GOES and the Helioseismic and Magnetic Imager (HMI) on the Solar Dynamics Observatory. We find that the \lya\ contrast in these WLFs ranges 0.8--28.5\% with a mean value of 7.0\%. Positive power-law relationships exist among peak enhancements in SXR, \lya, and WL. For most events, the \lya\ peak is nearly co-temporal with the peak of SXR time derivative, whereas the WL peak is either co-temporal with or lags those of \lya\ and SXR derivative. The \lya\ and WL rise times are similar ($\sim$3--4 min) and correlated. We also find that the radiated energy in \lya\ and HMI narrow-band WL has a positive power-law relationship with duration. In particular, the power-law index for the narrow-band WL is very close to 1/3 as predicted by magnetic reconnection theory. On average, the radiated energies in GOES \lya\ and SXR bands are approximately three orders of magnitude greater than the energy emitted in the continuum near 6173 \AA\ with a bandwidth of 1 \AA. Our findings provide new constraints on lower-atmosphere energy transport in solar flares and can serve as valuable references for modelling and interpreting the flares on solar-type stars.