Three‐dimensional Simulation of Gamma‐Ray Emission from Asymmetric Supernovae and Hypernovae

Hard X- and $\gamma$-ray spectra and light curves resulting from radioactivedecays are computed for aspherical (jet-like) and energetic supernova models(representing a prototypical hypernova SN 1998bw), using a 3D energy- andtime-dependent Monte Carlo scheme. The emission is characterized by (1) earlyemergence of high energy emission, (2) large line-to-continuum ratio, and (3)large cut-off energy by photoelectric absorptions in hard X-ray energies. Thesethree properties are not sensitively dependent on the observer's direction. Onthe other hand, fluxes and line profiles depend sensitively on the observer'sdirection, showing larger luminosity and larger degree of blueshift for anobserver closer to the polar ($z$) direction. Strategies to derive the degreeof asphericity and the observer's direction from (future) observations aresuggested on the basis of these features, and an estimate on detectability ofthe high energy emission by the {\it INTEGRAL} and future observatories ispresented. Also presented is examination on applicability of a gray effective$\gamma$-ray opacity for computing the energy deposition rate in the asphericalSN ejecta. The 3D detailed computations show that the effective $\gamma$-rayopacity $\kappa_{\gamma} \sim 0.025 - 0.027$ cm$^{2}$ g$^{-1}$ reproduces thedetailed energy-dependent transport for both spherical and aspherical(jet-like) geometry.Comment: 24 pages, 13 figures. Figure 7 added in the accepted version. ApJ, 644 (01 June 2006 issue), in press. Resolution of figures lower than the published versio