Correlation of hard X-ray and white light emission in solar flares

TL;DR

This study finds a significant correlation between hard X-ray emissions and white light in solar flares, indicating electrons around 50 keV are key to white light production, based on analysis of 43 flares with RHESSI and HMI data.

Contribution

It provides the first statistical analysis linking flare-accelerated electrons at ~50 keV to white light emission in solar flares.

Findings

Strong correlation (up to 0.68) between 30 keV X-ray flux and white light flux.

Electrons above ~50 keV show the strongest link to white light production.

Correlation decreases with higher electron energies, highlighting ~50 keV electrons as primary contributors.

Abstract

A statistical study of the correlation between hard X-ray and white light emission in solar flares is performed in order to search for a link between flare-accelerated electrons and white light formation. We analyze 43 flares spanning GOES classes M and X using observations from RHESSI (Reuven Ramaty High Energy Solar Spectroscopic Imager) and HMI (Helioseismic and Magnetic Imager). We calculate X-ray fluxes at 30 keV and white light fluxes at 6173 \r{A} summed over the hard X-ray flare ribbons with an integration time of 45 seconds around the peak hard-X ray time. We find a good correlation between hard X-ray fluxes and excess white light fluxes, with a highest correlation coefficient of 0.68 for photons with energy of 30 keV. Assuming the thick target model, a similar correlation is found between the deposited power by flare-accelerated electrons and the white light fluxes. The correlation coefficient is found to be largest for energy deposition by electrons above ~50 keV. At higher electron energies the correlation decreases gradually while a rapid decrease is seen if the energy provided by low-energy electrons is added. This suggests that flare-accelerated electrons of energy ~50 keV are the main source for white light production.