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Radioactive energies from unstable nuclei made in the ejecta of neutron starmergers play principal roles in powering kilonovae. In previous studiespower-law-type heating rates (e.g., ~ t^-1.3) have frequently been used, whichmay be inadequate if the ejecta are dominated by nuclei other than the A ~ 130region. We consider, therefore, two reference abundance distributions thatmatch the r-process residuals to the solar abundances for A >= 69 (lighttrans-iron plus r-process elements) and A >= 90 (r-process elements).Nucleosynthetic abundances are obtained by using free-expansion models withthree parameters: expansion velocity, entropy, and electron fraction.Radioactive energies are calculated as an ensemble of weighted free-expansionmodels that reproduce the reference abundance patterns. The results arecompared with the bolometric luminosity (> a few days since merger) of thekilonova associated with GW170817. We find that the former case (fitted for A>= 69) with an ejecta mass 0.06 M_sun reproduces the light curve remarkablywell including its steepening at > 7 days, in which the mass of r-processelements is ~ 0.01 M_sun. Two beta-decay chains are identified: 66Ni -> 66Cu ->66Zn and 72Zn -> 72Ga -> 72Ge with similar halflives of parent isotopes (~ 2days), which leads to an exponential-like evolution of heating rates during1-15 days. The light curve at late times (> 40 days) is consistent withadditional contributions from the spontaneous fission of 254Cf and a few Fmisotopes. If this is the case, the event GW170817 is best explained by theproduction of both light trans-iron and r-process elements that originate fromdynamical ejecta and subsequent disk outflows from the neutron star merger.

Physical conditions for the r-process I. radioactive energy sources of kilonovae