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A solar X-ray burst which evolves in time through two nonthermal phases is presented. The burst is considered to be bremostrablung from electrons accelerated in two stages in the solar atmosphere In the first stage, acceleration effectively to 100 keV occurs, perhaps by an induced electric field; in the second stage, the acceleration to higher energies could occur by a mechanism operating in a shock front.
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Frost et al. (1971) studied this question.
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