Background: Electron-capture reactions on iron-group nuclei play a crucial role in the late stages of massive star evolution. Since stellar evolution simulations depend on accurate electron-capture rates—which are highly sensitive to the detailed Gamow-Teller (GT) strength distributions—reliable theoretical models are essential. However, experimental data on GT strength distributions are scarce. High-resolution measurements are therefore vital for benchmarking and improving these theoretical calculations.

Purpose: To provide high-resolution data on Gamow-Teller strength distributions of iron-group nuclei and to compare these results with theoretical calculations within this mass region.

Methods: Differential cross sections for the ${}^{59}\mathrm{Co}(t,{}^3\mathrm{He}){}^{59}\mathrm{Fe}$ charge-exchange reaction at 115 MeV/u were measured using the S800 spectrometer. To resolve individual levels that are not distinguishable in the S800 particle singles data, coincident $\gamma$ rays from the ${}^{59}\mathrm{Fe}$ residual nucleus were detected by using the Gamma-Ray Energy Tracking In-beam Nuclear Array $\gamma$-ray tracking array.

Results: The Gamow-Teller transition strength distribution from the ground state of ${}^{59}\mathrm{Co}$ to ${}^{59}\mathrm{Fe}$ was extracted up to an excitation energy of 10 MeV. Additionally, transition strengths for several low-lying states were determined from coincident $\gamma$-ray measurements. Electron-capture rates calculated using the present data indicate that these low-lying states contribute significantly to the overall rates in relevant stellar environments. The experimental results show reasonable agreement with theoretical predictions based on both shell-model and projected shell-model calculations.

Conclusions: High-resolution data on Gamow-Teller strength distributions—particularly for individual low-lying states—are essential for accurately determining electron-capture rates in iron-group nuclei. Coincident $\gamma$-ray measurements provide a powerful tool for obtaining such detailed information. While the present work demonstrates that shell-model calculations successfully reproduce the experimental results, such comparisons are scarce and more experimental data are desirable.

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• Charge-exchange reactions
• Electron & muon capture
• Nuclear astrophysics
• Nuclear physics of explosive environments
• Nuclear reactions
• Nuclear structure & decays
• 59 ≤ A ≤ 89