Expectation for the Hard X-Ray and Gamma-Ray Emission from Pair-instability Supernovae

Abstract

Pair-instability supernovae (PISNe) are predicted thermonuclear explosions of massive stars with helium core masses exceeding ∼65 M _⊙ , and they synthesize substantial amounts of radioactive ^56 Ni ( M ( ^56 Ni) ∼ 60 M _⊙ in extreme cases). To investigate their observational signatures, we developed a multi-D Monte Carlo radiation transport code, assuming spherical symmetry in the background medium and the photon sources distribution, and performed simulations of gamma-ray and hard X-ray emissions from the decay chain ^56 Ni→ ^56 Co→ ^56 Fe. We find that key gamma-ray lines (847 and 1238 keV) from ^56 Co decay in the 130 M _⊙ helium core model can be detected up to 300–400 Mpc by next-generation MeV gamma-ray telescopes. In contrast, the signals from the 100 M _⊙ model remain below the detection limits. Our results provide the template for gamma-ray follow-up observations of PISNe. Considering theoretical predictions and observational constraints, we estimate PISN event rates within 300 Mpc to be approximately 0.01–0.1 events per year, highlighting their rarity but also emphasizing their feasibility as targets for future gamma-ray observations over the decade.

Keywords

• Supernovae
• X-ray astronomy
• Gamma-ray astronomy