Gamma-ray lines from asymmetric supernovae

Abstract

High energy emission from supernovae provide a direct window into the quantity and distribution of radioactive elements produced in these explosions. Combining supernova explosion calculations with 3D Monte Carlo gamma-ray transport, I have studied the effect mixing and asymmetries have on the hard X-ray and gamma-ray spectra. Two types of asymmetries (bipolar and unipolar) are investigated, the parameters of which are motivated by the most recent findings from multi-dimensional core-collapse supernova simulations. These bipolar and unipolar asymmetries are imposed artificially on 1-dimensional stellar progenitor structures and their evolution is followed using a 3-dimensional smoothed particle hydrodynamics (SPH) code. Global asymmetries in the explosion enhance the outward mixing of heavy elements such as 56Ni, reducing the observable emergence time for the hard X-ray continuum and gamma-ray line emission over that of symmetrically mixed models. The details of the velocity asymmetry lead to very different nickel distributions in the outer envelope. The high energy spectra resulting from these models predict an angular variation for the correspondence between the emergence time of the hard X-ray continuum and the broadening of the gamma-line profiles. The unipolar explosion models, in particular, demonstrate that redshifted gamma-ray line profiles are attainable at epochs where gamma-ray emission arises predominantly from the outer extent of the nickel distribution. The departure from a symmetric explosion scenario manifests itself most clearly in the extended nickel, making gamma-ray line observations an ideal probe of the initial explosion asymmetry.