BATSE All-Sky Plot of Gamma-Ray Burst Locations
The BATSE detectors, which continuously monitor the sky, have produced an extensive catalog of the puzzling, short-lived events known as gamma-ray bursts. Gamma-ray bursts last for fractions of a second to minutes. They appear to the BATSE detectors to pop off like flash bulbs at unexpected times from unexpected directions, flickering and then fading after briefly dominating the gamma-ray sky. The mystery of the origin of these bursts, first discovered by defense satellites in the 1960's, has been deepened by the more sensitive BATSE all-sky monitoring.
The above figure illustrates the locations of 2704 gamma-ray bursts detected by the BATSE instrument during nine years of observations. Statistical tests confirm that the bursts are isotropically distributed on the sky - no significant quadrupole moment or dipole moment is found. At the same time, a deficiency has been detected in the number of faint bursts, interpreted as an indication that the spatial extent of the burst distribution is limited and that BATSE sees the limit or edge of the distribution. The nature of the sources remains unknown. However, their isotropic distribution on the sky along with the deficiency of faint bursts can be naturally explained if the bursts are located at cosmological distances (far beyond the Milky Way). This interpretation has been confirmed in recent years via distance estimates for optical counterparts to gamma-ray bursts.
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