  Ghirlanda et al. (2004) derived the collimation-corrected energy E_gamma for
a sample of 15 bursts under the assumption of a homogeneous circumburst density
profile. They found a correlation (the so-called Ghirlanda correlation) between
E_gamma and the rest frame peak energy of the nuF_nu prompt spectrum (E_p).
Nava et al. (2006) showed that, assuming a circumburst density distribuited
with a r^-2 wind profile, the Ghirlanda correlation remains tight and becomes
linear. This implies that: i) it remains linear also in the comoving frame, no
matter the distribution of bulk Lorentz factors, ii) it entails that different
bursts have the same number of relevant photons. We have updated these findings
including recently detected bursts (21 in total), stressing the two important
implications.
