  The emission features observed in the X-ray afterglow of Gamma Ray Bursts are
extremely powerful. Since they last at least for several hours, they imply
energies of the order of 1e49 ergs. This in turn implies that the energy
contained in the illuminating continuum thought to be responsible of the line
production must exceed 1e51 ergs. This is a strong lower limit to the energy
reservoir of Gamma Ray Bursts, which is independent of collimation and beaming,
and bears important consequences on the possible collimation of the fireball
radiation and the density of the medium surrounding the burst.
