GRB progenitors at low metallicities
  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 Wolf--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:   - GRBs coming from WO--type (SNIc) WR stars are only produced at low Z (LMC or lower).   - The upper metallicity limit for GRBs is reduced to Z ~ 0.004 (SMC) when the effects of magnetic fields are included.   - GRBs are predicted from the second (and probably the first) stellar generation onwards. 
R. Hirschi, G. Meynet, A. Maeder