Explosive Nucleosynthesis Associated with Formation of Jet‐induced Gamma‐Ray Bursts in Massive Stars

We perform 2-dimensional relativistic hydrodynamical simulations in thecontext of collapsar model. Calculations of explosive nucleosynthesis are alsoaccomplished. We investigate the influence of the structure of the progenitorand energy deposition rate on the resulting explosive nucleosynthesis, assumingthat 56Ni is mainly synthesized in the jet launched by the neutrino heating. Weshow the amount of 56Ni is very sensitive to the energy deposition rate. Thuswe conclude that it is quite natural not to detect an underlying supernova insome X-ray afterglows as in GRB 010921. We also point out the possibility thatthe relative abundance of the elements with intermediate mass number such as Siand S in the X-ray afterglow of GRB 011211 may be naturally explained if theenergy deposition rate at the central engine is relatively long because littleamount of 56Ni should be synthesized under such an environment. If thisdiscussion is true, there should be correlation between the line features inthe X-ray afterglow and duration of the GRB. It should be noted that theduration of GRB 011211 is 270 seconds, making it the longest burst everobserved 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 thetype I collapsar model in which the energy deposition rate is relatively low(\dot{E} \sim 10^{51} erg/s) might have difficulty in reproducing the observedamount of 56Ni in a hypernova such as SN 1998bw. This means that the mechanismof the central engine of a hypernova accompanying GRB may be constrained by thediscussion of explosive nucleosynthesis.Comment: 29 pages and 20 postscript figures. Accepted for Publication in Astrophysical Journa