SIMBAD references

The recent discoveries of X-ray lines in the afterglows of gamma-ray bursts (GRBs) provide significant clues to the nature of GRB progenitors and central environments. However, the interpretation of iron lines as resulting from fluorescence or recombination requires a large amount of iron material. We argue that the very strong iron line could be attributed to an alternative mechanism: Cerenkov line emission, since relativistic electrons and dense medium exist near GRB sites. Therefore, broad iron lines are expected, and the line intensity will be nearly independent of the iron abundance; a medium with anomalously high Fe abundance is not required.