Distance Scale and Emission Model
Prior to this burst, astronomers had not reached consensus regarding how far away GRBs occur from Earth. Although the isotropic distribution of bursts suggested that they do not occur within the disk of the Milky Way, some astronomers supported the idea that they occur within the Milky Way's halo, concluding that the bursts are visibly faint because they are not highly energetic. Others concluded that GRBs occur in other galaxies at cosmological distances and that they can be detected because they are extremely energetic. The distance measurement and the calculations of the burst's total energy release unequivocally supported the latter theory, effectively ending the debate.
Throughout the month of May the radio scintillations became less noticeable until they ceased altogether. This implies that the radio source significantly expanded in the time that had passed since the burst was detected. Using the known distance to the source and the elapsed time before the scintillation ended, Frail calculated that the radio source had expanded at almost the speed of light. While various existing models already encompassed the notion of a relativistically expanding fireball, this was the first strong evidence to support such a model.
Read more about this topic: GRB 970508
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