Astronomy and Astrophysics – Astrophysics – Solar and Stellar Astrophysics
Scientific paper
2011-07-19
Astronomy and Astrophysics
Astrophysics
Solar and Stellar Astrophysics
3 figures, submitted to Astronomy and Astrophysics Letters
Scientific paper
The bulk of solar flare emission originates from very compact sources located in the lower solar atmosphere and seen in various wavelength ranges: near optical, UV, EUV, soft and hard X-rays, and gamma-ray emission, yet very few spatially resolved imaging observations to determine the structure of these regions exist. We investigate the above-the-photosphere heights of hard X-ray (HXR), EUV and white-light continuum sources in the low atmosphere and the corresponding densities at these heights. Simultaneous EUV/continuum images from SDO and HXR RHESSI images are compared to study a well observed gamma-ray limb flare. Using RHESSI X-ray visibilities we determine the height of the HXR sources as a function of energy above the photosphere. Co-aligning AIA/SDO and HMI/SDO images with RHESSI we infer, for the first time, the heights and characteristic densities of HXR, EUV and continuum sources in a flaring footpoint. 35-100 keV HXR sources are found at heights between 1.7 and 0.8 Mm above the photosphere, below the white-light continuum emission which appears at heights 1.5-3 Mm, and the peak of EUV emission originating near 3 Mm. The EUV emission locations are consistent with energy deposition from low energy electrons of ~12 keV occurring in the top layers of the fully ionized chromosphere/low corona and not by >20 keV electrons that produce HXR footpoints in the lower neutral chromosphere. The maximum of white-light emission appears between the HXR and EUV emission, presumably in the transition between ionized and neutral atmospheres suggesting free-bound and free-free continuum emission. We note that the energy deposited by low energy electrons is sufficient to explain the energetics of optical and UV emissions.
Battaglia Marina
Kontar Eduard P.
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