Explosive Nucleosynthesis Associated with Formation of Jet - induced GRBs in Massive Stars

We perform 2-dimensional relativistic hydrodynamical simulations in the context of collapsar model. Calculations of explosive nucleosynthesis are also accomplished. We investigate the influence of the structure of the progenitor and energy deposition rate on the resulting explosive nucleosynthesis, assuming that 56 Ni is mainly synthesized in the jet launched by the neutrino heating. We show the amount of 56 Ni is very sensitive to the energy deposition rate. Thus we conclude that it is quite natural not to detect an underlying supernova in some X-ray afterglows as in GRB 010921. We also point out the possibility that the relative abundance of the elements with intermediate mass number such as Si and S in the X-ray afterglow of GRB 011211 may be naturally explained if the energy deposition rate at the central engine is relatively long because little amount of 56 Ni should be synthesized under such an environment. If this discussion is true, there should be correlation between the line features in the X-ray afterglow and duration of the GRB. It should be noted that the duration of GRB 011211 is 270 seconds, making it the longest burst ever observed by Beppo-SAX although it suffers from the effect of red-shift (z host = 2.14), which supports our conclusion. Our results also suggest that the type I collapsar model in which the energy deposition rate is relatively low (˙ E ∼ 10 51 erg s −1) might have difficulty in reproducing the observed amount of 56 Ni in a hypernova such as SN 1998bw. This means that the mechanism of the central engine of a hypernova accompanying GRB may be constrained by the discussion of explosive nucleosynthesis.