COSMOLOGICAL RATES OF COALESCING NEUTRON-STARS AND GRB

Assuming that gamma-ray bursts (GRB) originate from binary neutron sta r (NS) or black holes (BH) merging in distant galaxies, theoretical lo g N-log S distributions for gamma-ray bursts (GRB) are calculated usin g the compact binaries coalescence rates computed for model galaxies w ith different star formation histories. A flat cosmological model (Ohm = 1) with different values of the cosmological constant Lambda is use d. The calculated source evolution predicts a 5-10 times increase of t he source statistics at count rates 3-10 times lower than the existing BATSE sensitivity limit. The most important parameter in fitting the 2nd BATSE catalogue is the initial redshift of star formation, which i s found to be z = 2 - 5 depending on a poorly determined average spec tral index of GRB.