6.2.3. Amati or *E* <sup>p</sup>–*E*iso Correlation

This correlation is of the form *E*<sup>p</sup> ∝ *E* 0.52 iso and shows that *E*iso is correlated with the rest-frame spectral peak energy, namely *E*<sup>p</sup> = *E* obs p (1 + *z*) [132]. Observations by *Swift* and *Fermi* detectors confirmed this correlation for LGRBs. An analogous *E*p–*E*iso correlation with a slope similar to that of LGRBs but a larger value of the normalization holds also for SGRBs, though with a much smaller data set [133]. Moreover, the *E*<sup>p</sup> − *E*iso correlation also holds within individual GRBs using time-resolved spectra, and the slopes are consistent with the correlation from time-integrated spectra. For details, see Ref. [130].
