Radioactive decay of specific heavy elements as an energy source for late-time kilonovae and potential James Webb Space Telescope observations

Revealing the temporal evolution of individual heavy elements synthesized in the merger ejecta from binary neutron star mergers not only improves our understanding of the origin of heavy elements beyond iron but also clarifies the energy sources of kilonovae. In this work, we present a comprehensive analysis of the temporal evolution of the energy fraction of each nuclide based on r-process nucleosynthesis simulations. The heavy elements dominating the kilonova emission within similar to 100 days are identified, including Sb-127, Sb-128, Sb-129, Sb-130, Te-129, I-132, Rn-222, Ra-223, Ra-224, and Ac-225. It is found that the late-time kilonova light curve (t greater than or similar to 20 days) is highly sensitive to the presence of the heavy element Ac-225 (with a half-life of 10.0 days). Our analysis shows that the James Webb Space Telescope (JWST), with its high sensitivity in the near-infrared band, is a powerful instrument for the identification of these specific heavy elements.