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The bulk of solar flare emission originates from very compact sources locatedin the lower solar atmosphere and seen in various wavelength ranges: nearoptical, UV, EUV, soft and hard X-rays, and gamma-ray emission, yet very fewspatially resolved imaging observations to determine the structure of theseregions exist. We investigate the above-the-photosphere heights of hard X-ray(HXR), EUV and white-light continuum sources in the low atmosphere and thecorresponding densities at these heights. Simultaneous EUV/continuum imagesfrom SDO and HXR RHESSI images are compared to study a well observed gamma-raylimb flare. Using RHESSI X-ray visibilities we determine the height of the HXRsources as a function of energy above the photosphere. Co-aligning AIA/SDO andHMI/SDO images with RHESSI we infer, for the first time, the heights andcharacteristic densities of HXR, EUV and continuum sources in a flaringfootpoint. 35-100 keV HXR sources are found at heights between 1.7 and 0.8 Mmabove the photosphere, below the white-light continuum emission which appearsat heights 1.5-3 Mm, and the peak of EUV emission originating near 3 Mm. TheEUV emission locations are consistent with energy deposition from low energyelectrons of ~12 keV occurring in the top layers of the fully ionizedchromosphere/low corona and not by >20 keV electrons that produce HXRfootpoints in the lower neutral chromosphere. The maximum of white-lightemission appears between the HXR and EUV emission, presumably in the transitionbetween ionized and neutral atmospheres suggesting free-bound and free-freecontinuum emission. We note that the energy deposited by low energy electronsis sufficient to explain the energetics of optical and UV emissions.

Height structure of X-ray, EUV and white-light emission in a solar flare