Binary stars as gamma ray burst progenitors

Using a stellar binary population synthesis code, we calculate the production rates and lifetimes of several types of possible gamma-ray burst (GRB) progenitors. We consider mergers of NS-NS, BH-NS, BH-WD systems and helium star mergers (a possible outcome of common envelope evolution of a compact object entering the envelope of a giant with a helium core). We discuss the viability of each GRB model, and alternatively assuming that all bursts are connected with binary mergers we constrain the required collimation of GRBs. Assuming that possible GRB progenitors are born in different types of galaxies we compute their spatial distribution and compare it with the observed locations of GRB afterglows within their hosts. We discuss constraints on the compact object merger model of GRBs imposed by this comparison and find that the observations of afterglows and their host galaxies imply that the helium mergers are the most promising binary progenitors of GRBs