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The 2014 March 29 X1 solar flare (SOL20140329T17:48) produced brightcontinuum emission in the far- and near-ultraviolet (NUV) and highly asymmetricchromospheric emission lines, providing long-sought constraints on the heatingmechanisms of the lower atmosphere in solar flares. We analyze the continuumand emission line data from the Interface Region Imaging Spectrograph (IRIS) ofthe brightest flaring magnetic footpoints in this flare. We compare the NUVspectra of the brightest pixels to new radiative-hydrodynamic predictionscalculated with the RADYN code using constraints on a nonthermal electron beaminferred from the collisional thick-target modeling of hard X-ray data fromRHESSI. We show that the atmospheric response to a high beam flux densitysatisfactorily achieves the observed continuum brightness in the NUV. The NUVcontinuum emission in this flare is consistent with hydrogen (Balmer)recombination radiation that originates from low optical depth in a densechromospheric condensation and from the stationary beam-heated layers justbelow the condensation. A model producing two flaring regions (a condensationand stationary layers) in the lower atmosphere is also consistent with theasymmetric Fe II chromospheric emission line profiles observed in the impulsivephase.

astrophysical journal/the astrophysical journal

The Atmospheric Response to High Nonthermal Electron Beam Fluxes in  Solar Flares I: Modeling the Brightest NUV Footpoints in the X1 Solar Flare  of 2014 March 29