Gamma ray bursts (GRBs) are associated with greatly intense explosions which occur almost entirely in distant galaxies. Because there are so many galaxies these explosions seem to occur with great regularity. We knew nothing about GRBs before the late 1960s when the conditions of the Nuclear Test Ban treaty appeared require monitoring.
When the Vela class satellites were launched they carried equipment able to detect gamma ray bursts, which were tell-tale signs of terrestrial nuclear explosions that could not be easily hidden. However, these satellites detected many bursts of gamma rays not coming from the Earth, but rather from elsewhere in the sky. They lasted for 5-10 milliseconds or up to several minutes. Initial bursts were followed by a longer afterglow which was not initially detected. The afterglow turned out to be longer wave lengths of light (x-ray, ultraviolet, visible, infrared, microwave and radio waves). These red shifted secondary waves put the distances from which GRBs were coming far outside our own galaxy to other nearby and distant galaxies.