Dominant Gamma-Ray Bursts Production in the Early Universe

It has been known that at least some of the observed gamma-ray bursts (GRBs) are produced at cosmological distances and the GRB production rate may follow the star formation rate. Here we report that the lower and upper distance limits to the GRB production are z approx. 0.22 and 8, respectively, as determined from BATSE's GRB fluence distribution. This result suggests that GRBs are no longer produced presently, and that the actual star formation rate peaks at much higher redshift and thus the 'dark ages' of the universe have ended much earlier than believed previously. We have also determined that the GRB opening angles follow an exponential distribution with a mean opening angle of about 0.03 radian. This study is supported in part by the Special Funds for Major State Basic Research Projects and by the National Natural Science Foundation of China. SNZ also acknowledges supports by NASA's Marshall Space Flight Center and through NASA's Long Term Space Astrophysics Program.