The Regulated NiCu Cycles with the New Cu-57(p,gamma)Zn-58 Reaction Rate and Its Influence on Type I X-Ray Bursts: the GS 1826-24 Clocked Burster

During the X-ray bursts of GS 1826-24, a "clocked burster", the nuclear reaction flow that surges through the rapid-proton capture process path has to pass through the NiCu cycles before reaching the ZnGa cycles that moderate further hydrogen burning in the region above the germanium and selenium isotopes. The Cu-57(p,gamma)Zn-58 reaction that occurs in the NiCu cycles plays an important role in influencing the burst light curves found by Cyburt et al. We deduce the Cu-57(p,gamma)Zn-58 reaction rate based on the experimentally determined important nuclear structure information, isobaric-multiplet-mass equation, and large-scale shell-model calculations. Based on the isobaric-multiplet-mass equation, we propose a possible order of 1(1)(+)- and 2(3)(+)-dominant resonance states and constrain the resonance energy of the 1(2)(+) state. The latter reduces the contribution of the 1(2)(+)-dominant resonance state. The new reaction rate is up to a factor of 4 lower than the Forstner et al. rate recommended by JINA REACLIB v2.2 at the temperature regime sensitive to clocked bursts of GS 1826-24. Using the simulation from the one-dimensional implicit hydrodynamic code KEPLER to model the thermonuclear X-ray bursts of the GS 1826-24 clocked burster, we find that the new Cu-57(p,gamma)Zn-58 reaction rate, coupled with the latest Ni-56(p,gamma)Cu-57 and Ni-55(p,gamma)Cu-56 reaction rates, redistributes the reaction flow in the NiCu cycles and strongly influences the burst ash composition, whereas the Cu-59(p,alpha)Ni-56 and Cu-59(p,gamma)Zn-60 reactions suppress the influence of the Cu-57(p,gamma)Zn-58 reaction and diminish the impact of nuclear reaction flow that bypasses the important Ni-56 waiting point induced by the Ni-55(p,gamma)Cu-56 reaction on the burst light curve.