Shortly after their discovery, astronomers realized there were at least two classes of GRB: short events (<2 seconds) and long events (>2 seconds). The long GRB are widely believed to by hypernova, the explosions of massive black holes in very distant galaxies. In fact, they are much further away than even Paczynski and his followers believed at the time of the debate. Consensus on short GRB has yet to be reached, though the neutron star-neutron star merger theory, no longer applicable to long GRB, is still in play for the short ones. Also, some small percentage of short GRB are certainly magnetar flares (such as the famous March 7, 1979 event) but in other nearby galaxies.
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