THE IMPLICATIONS OF DIRECT REDSHIFT MEASUREMENT OF GAMMA-RAY BURSTS

The recent discoveries of X-ray and optical counterparts for gamma-ray bursts (GRBs), and the possible discovery of a host galaxy, imply tha t direct measurement of the redshift of some GRB host galaxies is immi nent. We discuss the implications of such measurements. These measurem ents could enable us to determine the GRB luminosity distribution and the variation of the rate of GRBs with cosmic time and even, under fav orable circumstances, to estimate Omega. Using GRB 970508 alone, assum ing standard candles, and assuming the GRB source to be at the redshif t of the absorption line observed in the optical transient spectrum, w e constrain the intrinsic GRE evolution to rho(z) = (1+z)(-0.5+/-0.7).