Cosmological Constraints on the Host Halos of GRBs

The recently observed bright optical transients(OT) of high redshift GRBs indicate that they are in a violent dynamical state. We think it is reasonable to assume that the GRBs form in the environment of gravitationally collapsed halos of the cosmic matter field, and we investigate the basic parameters of the halos which are favored to host GRBs. If the harboring coefficient $f$ of GRBs per halo is weakly dependent on the mass of the halo, the redshift data of GRB OTs can yield significant constraints on the massive halos hosting GRBs. We show that, in the framework of popular cold dark matter (CDM) models, the GRB-favored environments are newly collapsed halos (i.e. their ages less than about $2 \times 10^9$ yr) with masses around $10^9$ $h^{-1}$ M$_{\odot}$. In this scenario, low redshift GRBs, if they exist, could not have the same cosmic origin as the high redshift ones. To fit with the observed rate of GRBs, we conclude that each GRB halo can host probably no more than one GRB event on average. This result implies that GRBs may be related to the merging of the halos.