About a million times more numerous than supernovae, they are thought to be the result of a collapse of super-massive stars or collision between compact objects like a black hole and a neutron star.  
A mass extinction at the end of the Ordovician period is suggested to have been caused by one of these.  In 2000, NASA launched the High Energy Transient Explorer 2 to detect them as their signals reach earth so ground observers can better study them.  About a million times more numerous than supernovae, they are thought to be the result of a collapse of super-massive stars or collision between compact objects like a black hole and a neutron star.  For ten points, name these astronomical phenomena that release a large amount of its namesake radiation.
A mass extinction at the end of the Ordovician period is suggested to have been caused by one of these.  
Gamma Ray Bursts or Gamma Ray Bursters