The nature of collapsar jets

The collapsar model explains the connection of long GRBs with dying massive stars. According to this model the GRB jet is formed at the center of a massive star, following it's core collapse. The jet then breaks out of the star and emits the gamma-ray photons far from the star, in an optically thin region. The breakout of the jet leaves a distinctive mark on the duration distribution of GRBs - it is flat at durations shorter than the typical breakout time of the jet. In this talk I will show that such a plateau exists in the duration distribution of all major GRB satellites. I will discuss the implications of this plateau on the composition of collapsar jets and the inferred properties of the progenitor. I will also show how this plateau can be used to better classify collapsar GRBs from non collapsars.