*3.3. Correlations between Spectral Peak Frequency and Energetics*

Other key features of the prompt emission, common to both long and short GRBs, are the observed correlations between the rest frame SED peak energy (*E*peak) and the burst energy or luminosity, considering isotropic emission (*E*iso-[191] and *L*iso [192]) or accounting for the GRB jet aperture angle (i.e., *E<sup>γ</sup>* = *E*iso(1 − cos *θ*j), see [21]). Short and long GRBs, owing to their different duration, follow two nearly parallel correlations in the *E*peak − *E*iso plane while they show a similar *E*peak − *L*iso correlation [193,194]. While these correlations may be subject to instrumental selection effects, their physical nature is corroborated by the existence, within individual GRBs, of similar relations between the same observables as a function of time along the prompt emission duration [157,195].
