3 Conclusions

We discussed three possible mechanisms for the production of a strong iron line, visible during the X-ray afterglows of GRB. All mechanisms require the presence of a large amount of iron in a compact region. The remnant of a supernova exploded a few months before the burst matches the required matter and size.

We find that the multiple ionization and recombination scenario has difficulties in reconciling the low temperature required to have a fast recombination with the large heating due to the burst flux. On the other hand, we believe that the other two alternatives (i.e. thermal emission and reflection) are promising and not mutually exclusive.

In the reflection scenario, afterglow spectra should show the typical hardening of the spectrum above a few keV, and the line duration should be short.