We perform multi-dimensional, time-dependent radiation transfer simulations for hard X-ray and γ-ray emissions, following radioactive decays of 56Ni and 56Co, for two-dimensional delayed-detonation models of Type Ia supernovae (SNe Ia). The synthetic spectra and light curves are compared with the sensitivities of current and future observatories for an exposure time of 106 s. The non-detection of the γ-ray signal from SN 2011fe at 6.4 Mpc by SPI on board INTEGRAL places an upper limit on the mass of 56Ni of 1.0 M ☉, independently from observations in any other wavelengths. Signals from the newly formed radioactive species have not yet been convincingly measured from any SN Ia, but future X-ray and γ-ray missions are expected to deepen the observable horizon to provide high energy emission data for a significant SN Ia sample. We predict that the hard X-ray detectors on board NuStar (launched in 2012) or ASTRO-H (scheduled for launch in 2014) will reach to SNe Ia at ~15 Mpc, i.e., one SN every few years. Furthermore, according to the present results, the soft γ-ray detector on board ASTRO-H will be able to detect the 158?keV line emission up to ~25 Mpc, i.e., a few SNe Ia per year. Proposed next-generation γ-ray missions, e.g., GRIPS, could reach to SNe Ia at ~20-35 Mpc by MeV observations. Those would provide new diagnostics and strong constraints on explosion models, detecting rather directly the main energy source of supernova light.
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