Explosive Nucleosynthesis in GRB Jets Accompanied by Hypernovae

Abstract

Two-dimensional hydrodynamic simulations are performed to investigate explosive nucleosynthesis in a collapsar using the model of MacFadyen and Woosley. It is shown that 56Ni is not produced in the jet of the collapsar sufficiently to explain the observed amount in a hypernova when the duration of the explosion is ∼10 s. Even though a considerable amount of 56Ni is synthesized if all the explosion energy is deposited initially, the opening angles of the jets become too wide to realize highly relativistic outflows. From these results, it is concluded that the origin of 56Ni in hypernovae associated with GRBs is not the explosive nucleosynthesis in the jet. We consider that the idea that the origin is the explosive nucleosynthesis in the accretion disk is more promising. We also show that the explosion becomes bipolar naturally because of the deformed progenitor. This fact suggests that the 56Ni is synthesized in the accretion disk and conveyed as outflows blown along the rotation axis, which will explain the line features of SN 1998bw and the double-peaked line features of SN 2003jd. Some fraction of the gamma-ray lines from 56Ni decay in the jet will appear without losing their energies as long as the jet is a relativistic flow, which may be observed as relativistically Lorentz-boosted line profiles in the future. We show that the abundance of nuclei whose mass number ∼40 in the ejecta depends sensitively on the energy deposition rate. So it may be determined by observations of chemical composition in metal-poor stars which model is the proper one. © 2006. The American Astronomical Society. All rights reserved.