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Relationship between non-thermal electron energy spectra and GOES classes

“…A power-law dependence of the emitted spectrum implies that the non-thermal electrons have a power law energy distribution (Brown 1971;Tandberg-Hanssen & Emslie 1988) and this in turn requires a low energy cut-off E c to the electron spectrum to prevent an infinite total electron energy. A arbitrary value of E c has been defined by numerous authors between 15 and 25 keV (see e.g., McDonald et al 1999 and references therein). Thus, E c occupies the energy range where thermal emission can dominate and so it is very difficult to determine its correct value from observations.…”

“…We estimated E c as follows. First, we derived low energy cut-offs of the energy spectra using the slightly modified semi-analytical model of McDonald et al (1999). While these authors used a fixed value of E c (equal to 20 keV) for all flares, we calculated E c for each flare using an iterative method.…”

“…Many flares exhibit low SXR emission (as indicated by their GOES emission), but strong, HXR emission above 30 keV (McDonald et al 1999;Gburek & Siarkowski 2002;Qiu et al 2004;Siarkowski et al 2006). These events are commonly called "non-correlated" flares.…”

“…These events are commonly called "non-correlated" flares. Analytical estimations by McDonald et al (1999) demonstrated that, in these flares, only a small part of the total energy carried by the nonthermal electrons is transferred to the ambient material during the chromospheric evaporation process. Even so, analysis of the HXR emission of these flares allows one to estimate the energy flux of non-thermal electrons and numerically simulate the energy losses and hydrodynamic effects of the chromospheric evaporation, thus allowing investigations of the energy budgets of the solar flares.…”

“…Details are given in Table 1. Five flares were analysed by McDonald et al (1999) (four being correlated and one non-correlated), a further seven flares were taken from the HXT Flare Catalogue (Sato et al 2006), four being correlated and three non-correlated. The correlated and non-correlated events are denoted in Table 1 with letters C and N, respectively.…”