Features of Nucleosynthesis and Neutrino Emission from Collapsars

Abstract

In this study we present two indicators that will reflect the difference between collapsars and normal collapse-driven supernovae. They are products of explosive nucleosynthesis and neutrino emission. In the collapsar model, it is natural to consider that the product of explosive nucleosynthesis depends on the zenith angle because the system becomes highly asymmetric in order to generate a fire ball. We also consider the detectability of the HNRs which is located nearby our Galaxy. As a result, the number of the HNRs is estimated to be 5 $\times$ ($10^2$ -- $10^{-3}$), whose chemical composition can be spatially resolved. Using the optimistic estimate, more HNRs will be found and it will be possible to discuss on the chemical composition statistically. As for the energy spectrums of neutrinos, they are not thermalized in a collapsar because the density of the accretion disk is much lower than that of a neutron star. The energy spectrums of (anti-)electron neutrinos from hypernovae will be mainly determined by the process of electron (positron) capture on free proton (neutron). It is also noted that high energy tail is not dumped in the case of hypernovae because the density of emitting region is low. Total energy of neutrino from hypernovae will depend on a lot of physical parameters such as total accreting mass and mass accretion rate, which are quite contrary to the situation of the normal collapse-driven supernovae. Therefore there will be a large variety of total neutrino's energies among collapsars. In the case of SN 1998bw, we think that the matter around the equatorial plane might be ejected from the system, which resulted in the formation of relatively weak jets and faint GRB 980425.

12 pages and 3 postscript figures

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