How did they work? An identical detector was mounted on each corner of the CGRO. When gamma-ray radiation from a burst arrived at the satellite, only three or four detectors would see it, the others being in the shadow on the other side of the spacecraft. So the first thing you would notice in the data is a dramatic flare of gamma-rays that only a few of the detectors (but more than one!) measured.

However, there is more that can be learned! The efficiency of the detector is strongly dependent upon the angle at which the radiation strikes it. That means that a strong burst coming in at a high angle would produce a weaker signal than a weaker burst hitting the detector face-on. Since multiple detectors observe the same burst at different angles, they will measure signals of different strengths. There is only one place on the sky from which a burst can produce the measured signals. Comparing the strengths of the different signals allows you to determine just what that position is, to within some amount of error. This amount was effectively never better than about ten degrees across, which is twenty times as wide as the full moon.

However, given the thousands of bursts that were detected, although no single burst could be localized with pinpoint accuracy, strong statements could be made about their collective properties. Among the discoveries made and/or confirmed by BATSE data are:

• There are two classes of bursts: more than a few seconds, and less than one second
• Bursts are spread smoothly across the sky. They do not clump along the Milky Way, nor do we see any cluster around nearby galaxies.
• There are far fewer faint bursts than you would expect to see if they were spread smoothly throughout infinite space.

The Compton Gamma-Ray Observatory was sadly de-orbited in June of 2000, falling into the Pacific Ocean. See also:

• The BATSE Homepage