Summary of Early Observations

Gamma ray bursts occur on average about once per day. The adjacent map represents the entire sky in galactic coordinates (Ref). It shows the position of about 800 gamma ray bursts detected by the BATSE experiment (right panel). In this map, spot size is proportional to peak flux during the gamma ray burst and color indicates the average energy, with bluer dots highest in energy.

The following image shows the position of 2000 bursts detected by BATSE, with no indication of strength or average energy (Ref)

Before the systematic BATSE observations, a common hypothesis was that gamma ray bursts occurred in the disk of our galaxy. The above sky maps contradict this hypothesis because it indicates that the distribution of bursts is isotropic (no preferred direction). This tells us that either the gamma ray bursts come from events at great distances (cosmological distances), or that they come from events in the more spherical halo of our galaxy.