How Far Away Are Gamma-Ray Bursters?

The positions of over 1000 gamma-ray bursts detected with the BATSEexperiment on board of the Compton Gamma Ray Observatory are uniformly andrandomly distributed in the sky, with no significant concentration to thegalactic plane or to the galactic center. The strong gamma-ray bursts have anintensity distribution consistent with a number density independent of distancein Euclidean space. Weak gamma-ray bursts are relatively rare, indicating thateither their number density is reduced at large distances or that the space inwhich they are distributed is non-Euclidean. In other words, we appear to be atthe center of a spherical and bounded distribution of bursters. This isconsistent with the distribution of all objects that are known to be atcosmological distances (like galaxies and quasars), but inconsistent with thedistribution of any objects which are known to be in our galaxy (like stars andglobular clusters). If the bursters are at cosmological distances then theweakest bursts should be redshifted, i.e. on average their durations should belonger and their spectra should be softer than the corresponding quantities forthe strong bursts. There is some evidence for both effects in the BATSE data. At this time the cosmological distance scale is strongly favored over thegalactic one, but is not proven. A definite proof (or dis-proof) could beprovided with the results of a search for very weak bursts in the Andromedagalaxy (M31) with an instrument $ \sim 10 $ times more sensitive than BATSE. If the bursters are indeed at cosmological distances then they are the mostluminous sources of electromagnetic radiation known in the universe. At thistime we have no clue as to their nature, even though well over a hundredsuggestions were published in the scientific journals. An experiment providing