2022ApJ...929...72L

We reassess the ⁶⁵As(p,γ)⁶⁶Se reaction rates based on a set of proton thresholds of ⁶⁶Se, S_p(⁶⁶Se), estimated from the experimental mirror nuclear masses, theoretical mirror displacement energies, and full pf-model space shell-model calculation. The self-consistent relativistic Hartree-Bogoliubov theory is employed to obtain the mirror displacement energies with much reduced uncertainty, and thus reducing the proton-threshold uncertainty up to 161 keV compared to the AME2020 evaluation. Using the simulation instantiated by the one-dimensional multi-zone hydrodynamic code, KEPLER, which closely reproduces the observed GS 1826-24 clocked bursts, the present forward and reverse ⁶⁵As(p,γ)⁶⁶Se reaction rates based on a selected S_p(⁶⁶Se) = 2.469 ± 0.054 MeV, and the latest ²²Mg(α,p)²⁵Al, ⁵⁶Ni(p,γ)⁵⁷Cu, ⁵⁷Cu(p,γ)⁵⁸Zn, ⁵⁵Ni(p,γ)⁵⁶Cu, and ⁶⁴Ge(p,γ)⁶⁵As reaction rates, we find that though the GeAs cycles are weakly established in the rapid-proton capture process path, the ⁶⁵As(p,γ)⁶⁶Se reaction still strongly characterizes the burst tail end due to the two-proton sequential capture on ⁶⁴Ge, not found by the Cyburt et al. sensitivity study. The ⁶⁵As(p,γ)⁶⁶Se reaction influences the abundances of nuclei A = 64, 68, 72, 76, and 80 up to a factor of 1.4. The new S_p(⁶⁶Se) and the inclusion of the updated ²²Mg(α,p)²⁵Al reaction rate increases the production of ¹²C up to a factor of 4.5, which is not observable and could be the main fuel for a superburst. The enhancement of the ¹²C mass fraction alleviates the discrepancy in explaining the origin of the superburst. The waiting point status of and two-proton sequential capture on ⁶⁴Ge, the weak-cycle feature of GeAs at a region heavier than ⁶⁴Ge, and the impact of other possible S_p(⁶⁶Se) are also discussed.