A gamma-ray burst （GRB） is an extremely luminous flash of gamma rays that occurs as the result of an explosion, and is thought to be associated with the formation of a black hole. Most GRBs are billions of light years away from Earth, implying that the explosions are both extremely energetic （a typical burst releases as much energy in a few seconds as the Sun will in its entire 10-billion-year lifetime） and extremely rare （a few per galaxy per million years）. Researches on GRBs have attracted wide attention. For experts on accretion disks,
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