Talk:The Rise and Fall of The Low Energy Cut Off

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It appears to me a bit premature...

It appears to me a bit premature to say that the low-energy cutoff issue is dead: As pointed out in Holman et al. (2003) the "traditional" method yields a lower limit of 2.6x10^31 ergs in injected non-thermal electrons, a factor 3 or so above the instantaneous thermal energy content, a fact often observed in flares (see e.g. Emslie et al., 2004; Saint-Hilaire et al., 2005; ...). Using Emslie's "Death to the low-energy cutoff" approach (Emslie, 2003), and using for kT that given by isothermal fitting of the X-ray spectrum, Gordon Holman finds 4x10^34 ergs as the upper limit on the energy in injected non-thermal electrons. I.e. *three* orders of magnitude more. Where does all that energy go to? Which method is closest to the Truth? Assuming this is indeed too much energy, it is clear that we need another, higher, kT value than the one given by isothermal fitting.

I think Emslie (2003) is a definite step forward, but might have simply pushed the problem sideways for observers interested in flare energetics: instead of determining a proper low-energy cutoff, it seems it is an appropriate super-hot kT that has to be determined...

--pshilaire 18 November 2008 (UTC)

It is better to start from...

It is better to start from which low energy cut off is actually dead. In the nugget, the low energy cut off in the mean electron flux spectrum demanded by the observations is declared "dead". The low energy cut off in the injected electron spectrum, which is related to the injected electron energy, is derived under some assumptions about the propagation of electrons. For example, Holman et al (2003) follow thick target model assuming that electrons are affected only by binary collisions and no magnetic field, no plasma waves, no return current, etc. Therefore, for such a simple model, it is next to a miracle that something is off only by three orders of magnitude. The absence of the observational evidences for the low energy cut off in the mean electron spectrum (model independent in terms of electron transport) might push the development/use of more sophisticated transport models to find "the closest to the Truth" values.

--Ekontar 23:14, 18 November 2008 (UTC)