They were determined to originate from very distant, young galaxies and are speculated to be narrow-angle expulsions of energy from supernovas or neutron star compressions.  
These were first discovered in 1967 by military satellites looking for radiation from tests of nuclear weapons, when they were determined to originate from deep space.  The US launched the Compton Observatory, which was later linked to the Italian-Dutch BeppoSAX x-ray telescope as well as optical telescopes, to search for their optical counterpart sources.  They were determined to originate from very distant, young galaxies and are speculated to be narrow-angle expulsions of energy from supernovas or neutron star compressions.  FTP, identify this phenomenon in which high-energy photons are intensely emitted for a very brief period, often abbreviated GRB.
These were first discovered in 1967 by military satellites looking for radiation from tests of nuclear weapons, when they were determined to originate from deep space.  
gamma ray bursts or bursters (accept GRBs before it's given)