This empirical relationship is called the “Neupert effect”. An example is presented in Figure 12. Already Neupert (1968) suggested that there may be a direct causal relation between the energetic electrons and the thermal plasma: the soft X-rays may originate chiefly from a plasma heated by the accumulated energy deposited through flare accelerated electrons. It should be remarked here that Equation 1 is only an approximation and that the correspondence with theory works only if cooling (by conduction or radiation) is negligible.
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