2019/06/13 by Markus Aschwanden, Eduard P. Kontar, Natasha L. S. Jeffrey · 2 citations
Physics and Astronomy · #astro-ph.SR
paper · pdf · doi:10.3847/1538-4357/ab2cd4
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arxiv created 2019/06/13 · arxiv updated 2019/08/14
One of the key problems in solar flare physics is the determination of the low-energy cut-off; the value that determines the energy of nonthermal electrons and hence flare energetics. We discuss different approaches to determine the low-energy cut-off in the spectrum of accelerated electrons: (i) the total electron number model, (ii) the time-of-flight model (based on the equivalence of the time-of-flight and the collisional deflection time); (iii) the warm target model of Kontar et al.~(2015), and (iv) the model of the spectral cross-over between thermal and nonthermal components. We find that the first three models are consistent with a low-energy cutoff with a mean value of ≈ 10 keV, while the cross-over model provides an upper limit for the low-energy cutoff with a mean value of ≈ 21 keV. Combining the first three models we find that the ratio of the nonthermal energy to the dissipated magnetic energy in solar flares has a mean value of qE=0.57±0.08, which is consistent with an earlier study based on the simplified approximation of the warm target model alone (qE=0.51±0.17). This study corroborates the self-consistency between three different low-energy cutoff models in the calculation of nonthermal flare energies.