Left: total “bolometric” emitted energy, E_opt, estimated from the CoRoT lightcurves (see text) vs. energy emitted in the 0.5–8.0 keV band, E_X. Green and red circles indicate flares from Class III and Class II stars, respectively. Filled circles refer to the flares in our main samples, empty ones to flares with particularly uncertain estimates. The dashed lines shows the unit relation, while the solid lines show the results of six different linear fits (in the log–log plane) performed with different methods, and whose parameters are shown in the upper part of the panel along with the 1σ dispersion of residuals. The fitting methods are: (1) Ordinary Least Squares Y vs. X, (2) Ordinary Least Squares X vs. Y, (3) Ordinary Least Squares Bisector, (4) Orthogonal Reduced Major Axis, (5) Reduced Major-Axis, (6) Mean ordinary Least Squares. Right: same as the plot on the left, but for peak luminosities instead of energies.