Gamma-Ray Signatures of Supernovae and Hypernovae

Abstract

We review the characteristics of nucleosynthesis and radioactivities in 'Hypernovae', i.e., supernovae with very large explosion energies ($ \gsim 10^{52} $ ergs) and their $\gamma$-ray line signatures. We also discuss the ${}^{44}$Ti line $\gamma$-rays from SN1987A and the detectability with INTEGRAL. Signatures of hypernova nucleosynthesis are seen in the large [(Ti, Zn)/Fe] ratios in very metal poor stars. Radioactivities in hypernovae compared to those of ordinary core-collapse supernovae show the following characteristics: 1) The complete Si burning region is more extended, so that the ejected mass of ${}^{56}$Ni can be much larger. 2) Si-burning takes place in higher entropy and more $\alpha$-rich environment. Thus the ${}^{44}$Ti abundance relative to ${}^{56}$Ni is much larger. In aspherical explosions, ${}^{44}$Ti is even more abundant and ejected with velocities as high as $\sim$ 15,000 km s${}^{-1}$, which could be observed in $\gamma$-ray line profiles. 3) The abundance of ${}^{26}$Al is not so sensitive to the explosion energy, while the ${}^{60}$Fe abundance is enhanced by a factor of $\sim$ 3.

Invited talk at the ``GAMMA2001'' Symposium, April 4-6, 2001, Baltimore. To be published in ``Gamma-Ray Astronomy 2001'' (American Institute of Physics)

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