Single star progenitors of long gamma-ray bursts

We present grids of massive star evolution models at four different metallicities (). The effects of rotation on the stellar structure and the transport of angular momentum and chemical elements through the Spruit-Tayler dynamo and rotationally induced instabilities are considered. After discussing uncertainties involved with the adopted physics, we elaborate the final fate of massive stars as a function of initial mass and spin rate, at each considered metallicity. In particular, we investigate for which initial conditions long gamma-ray bursts (GRBs) are expected to be produced in the frame of the collapsar model. Then, using an empirical spin distribution of young massive metal-poor stars and a specified metallicity-dependent history of star-formation, we compute the expected GRB rate as function of metallicity and redshift based on our stellar evolution models. The GRB production in our models is limited to metallicities of , with the consequence that about 50% of all GRBs are predicted to be found at redshifts above , with most supernovae occurring at redshifts below . The average GRB/SN ratio predicted by our model is about globally, and at low redshift. Future strategies for testing the considered GRB progenitor scenario are briefly discussed.

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