In Figure 5.1 is shown the distribution of the arrival directions of 1429 GRBs from BATSE. Each point in the plot is located at the galactic coordinates of the arrival direction of one GRB, and the graphic representation is given in the Aitoff-Hammer projection (characterized by the equivalence between solid angle and area). As can be seen by eye, and tested through statistical methods, there is no evidence for any kind of anisotropy in the angular distribution.
Since any class of galactic object has a characteristic distribution in this representation (for instance, the youngest stars are mainly distributed in the galactic plane, where the spiral arms are and where the star formation is confined), this characteristic of the GRBs is a first indication that the GRBs are not easily associated to any known class of objects in our Galaxy. Moreover, given that our Solar System is located about 9 kPc away from the center of the Galaxy (that has a diameter of about 23 kPc), then the measurement of the isotropy can exclude an origin of the GRBs from sources uniformly distributed in the Galaxy. In fact, in this case one should observe a dipole momentum in the angular distribution. The upper limit to the dipole anisotropy is 1.5 %.