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tokens: of the Ramaty ( 1969 ) model fit to the radio spectra. Both spectral indices are listed on Table 2 . As can be seen from these results, the spectral indices of the energy distribution of the radio emitting electrons agree reasonably well with that of the hard X-ray producing electrons, when considering photons with energies higher than 400–700 keV or, conversely, electrons with energies ≥1 MeV. The reconstructed energy spectra of the accelerated electrons can be represented by a broken power law with break energy around 500 keV, and spectral index δ = 4 below this energy and δ = 2 above (see Figure 6 ). The photons detected below energies of ∼500 keV (representing E 2 ) are produced by lower-energy electrons with an energy distribution index of δ ≈ 4, whereas the higher-energy hard X-rays and radio emission (microwaves and millimeter waves) are generated by electrons with energies ≥1 MeV and δ ≈ 2. Previous works, such as Silva et al. ( 2000 ), showed that the spectral indices for the population of accelerated electrons emitting the radio and the X-rays do not match, with the radio index being harder than that of the X-rays by approximately 2 units. The authors explained this discrepancy by the fact that the radio emission is produced by higher-energy electrons than the X-rays, and that the common accelerated electron population has a power-law energy distribution that breaks up above 300 KeV. Since the hard X-rays analyzed in Silva et al. ( 2000 ) had energies lower than ∼200 keV, the results are in agreement with those presented here for the SOL2013-05-13 flare, as well as the two discrepancies in the spectral indices of hard X-rays and radio. Moreover, Vestrand ( 1988 ) and Dennis ( 1988 ) report giant flares observed in hard X-rays with energies larger than 1 MeV that showed a breakup in their photon spectra at ∼300 keV. More recently, from the analysis of an X8.2 solar flare detected in hard X-rays by RHESSI, Ning et al. ( 2019 ) found a broken-up power-law spectra originating from a coronal source. However, the break energy was only about 50 keV and the harder spectral photon index was ∼3. There are basically three possible explanations for electrons to exhibit such a broken-up power-law energy distribution. The first is that there are two components, or sources, of energetic electrons that were produced by two different acceleration mechanisms (Silva et al. 2000 ; Krucker et al. 2008 ). However, to produce a similar temporal evolution in radio and hard X-ray emission, there must be a close link between these two acceleration mechanisms. Alternatively, the second possibility is that the difference in spectral indices is due to physical characteristics of a certain acceleration mechanism and/or a transport process of electrons such as diffusive shock acceleration (Li et al. 2013 ), where a hardening of the spectrum occurs around 500–600 keV, or stochastic acceleration due to wave–particle interactions in the presence of Coulomb collisions