Gamma-Ray Bursts: Astronomical Constraints

After presenting a short history of gamma-ray burst (GRB) studies, we discuss the current constraints on GRB models which follows from astronomical observations. We concentrate on the energetics of the GRBs with known redshifts and the association of the well-localized GRBs with star forming regions in remote galaxies. We also discuss implications of the observed GRB rate. Arguments are given favoring possible connection of GRBs with core collapse of massive Wolf-Rayet stars. The possibility of GRB to be a transient phenomenon in the early history of galactic star formation related to evolution of very massive metal-free stars is briefly outlined.