Gamma-Ray Bursts (GRBs)
Short (~ a few s), bright bursts of gamma-rays
Later discovered with X-ray and optical afterglows lasting several hours – a few days
GRB of May 10, 1999:  1 day after the GRB
2 days after the GRB
Many have now been associated with host galaxies at large (cosmological) distances.
Probably related to the deaths of very massive (> 25 Msun) stars.
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