Distribution of black hole binaries around galaxies

Compact object mergers are one of the favorite models of GRBs. It has been noted that in contrast to the collapsars, compact object mergers do not nec essarily take place in the host galaxies, and may travel outside of them. W ith the discovery of afterglows and identification of host galaxies one can measure the distribution of GRBs with respect to their host galaxies. This distribution has been calculated using different population synthesis code s, and for different galactic potentials (Bloom et al., 1999; Bulik et al., 1999a; Fryer et al., 1999). In this paper we compare the distributions of different types of compact object binaries: double neutron star systems (NS -NS), black hole-neutron star systems (BH-NS) and double black holes (BH-BH ). We calculate the orbits and distributions of the projected distances on the sky for two extreme cases: a massive galaxy like the Milky Way, and emp ty space (corresponding to e.g. a globular cluster), and consider a wide ra nge of possible kick velocity distributions. We find that BH-NS are more li kely gamma-ray burst counterparts, since they lie close to the host galaxie s, contrary to the NS-NS binaries.