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We present a novel observation of the white-light flare (WLF) continuum,which was significantly enhanced during the X1 flare on March 29, 2014(SOL2014-03-29T17:48). Data from the Interface Region Imaging Spectrograph(IRIS) in its NUV channel show that at the peak of the continuum enhancement,the contrast at the quasi-continuum window above 2813 \AA\ reached 100 - 200 %and can be even larger closer to the Mg II lines. This is fully consistent withthe hydrogen recombination Balmer continuum emission, which follows animpulsive thermal and non-thermal ionization caused by the precipitation ofelectron beams through the chromosphere. However, a less probable photosphericcontinuum enhancement cannot be excluded. The light curves of the Balmercontinuum have an impulsive character with a gradual fading, similar to thosedetected recently in the optical region on Hinode/SOT. This observationrepresents a first Balmer-continuum detection from space far beyond the Balmerlimit (3646 \AA), eliminating seeing effects known to complicate the WLFdetection. Moreover, we use a spectral window so far unexplored for flarestudies, which provides the potential to study the Balmer continuum, as well asmany metallic lines appearing in emission during flares. Combined with futureground-based observations of the continuum near the Balmer limit, we will beable to disentangle between various scenarios of the WLF origin. IRISobservations also provide a critical quantitative measure of the energyradiated in the Balmer continuum, which constrains various models of the energytransport and deposition during flares.

Hydrogen Balmer Continuum in Solar Flares Detected by the Interface Region Imaging Spectrograph (IRIS)