Gamma ray bursts (GRBs) are the most explosive and brightest known photon sources in the universe. The initial bursts of GRBs found so far typically have a spectral peak between ∼100 keV and 1 MeV. Most of their gamma ray prompt emissions last for ∼100 s or less. The jets ejected from ‘the central engine’ are thought to be responsible for these bursts. According to the currently accepted scenario, a black hole produced by the merger of compact objects (such as black holes and/or neutron stars) is responsible for shorter bursts while collapse of a massive star directly to a black hole produces longer bursts, although clear-cut distinction may not exist. In this paper, we consider the latter case, a collapsar model responsible for longer GRBs. They are more interesting in the sense that they are more energetic and hence their studies can be extended to first Population III GRBs, which may give some constraints on the understanding of the early universe. In this paper, we are interested mainly in the “central engine”, the region created by the collapse of a rotating massive star to a spinning black hole and its surrounding area created by the stellar remnant because the conditions of the jet propagation change once they are outside in the interstellar medium. We first follow the process of how a progenitor massive star collapses and forms a central disk-black hole system, how powerful jets are produced and ejected from that system, and how the jets propagate and penetrate the surrounding stellar medium. The continued journey of the jets outside the star and the mechanisms for GRB emissions are outside the scope of this short paper.
