GRB progenitors at low metallicities

摘要

We calculated pre-supernova evolution models of single rotating massive stars. These models reproduce observations during the early stages of the evolution very well, in particular Woli^Rayet (WR) populations and ratio between type II and type Ib,c supernovae at different metallicities (Z). Using these models we found the following results concerning long and soft Gamma-Ray Burst (GRB) progenitors: a) GRBs coming from WO-type (SNIc) WR stars are only produced at low Z (ZLMC = 0.008 or lower), b) The upper metallicity limit for GRBs is reduced to Z ~ 0.004 (SMC) when the effects of magnetic fields are included, c) GRBs are predicted from the second (and probably the first) stellar generation onwards.