The Radiated Energy Budget of Chromospheric Plasma in a Major Solar Flare Deduced From Multi-Wavelength Observations

Abstract

This paper presents measurements of the energy radiated by the lower solar atmosphere, at optical, UV, and EUV wavelengths, during an X-class solar flare (SOL2011-02-15T01:56) in response to an injection of energy assumed to be in the form of nonthermal electrons. Hard X-ray observations from RHESSI were used to track the evolution of the parameters of the nonthermal electron distribution to reveal the total power contained in flare accelerated electrons. By integrating over the duration of the impulsive phase, the total energy contained in the nonthermal electrons was found to be $>2\times 10^{31}$ erg. The response of the lower solar atmosphere was measured in the free-bound EUV continua of H I (Lyman), He I, and He II, plus the emission lines of He II at 304Ã and H I (Ly$\hat{I}\pm$) at 1216Ã by SDO/EVE, the UV continua at 1600Ã and 1700Ã by SDO/AIA, and the WL continuum at 4504Ã , 5550Ã , and 6684Ã , along with the Ca II H line at 3968Ã using Hinode/SOT. The summed energy detected by these instruments amounted to $\sim 3\times 10^{30}$ erg; about 15% of the total nonthermal energy. The Ly$\hat{I}\pm$ line was found to dominate the measured radiative losses. Parameters of both the driving electron distribution and the resulting chromospheric response are presented in detail to encourage the numerical modelling of flare heating for this event, to determine the depth of the solar atmosphere at which these line and continuum processes originate, and the mechanism(s) responsible for their generation.

14 pages, 18 figures. Accepted for publication in Astrophysics Journal