Advancement of Photospheric Radius Expansion and Clocked Type-I X-Ray Burst Models with the New ${}^{22}$Mg$(\alpha ,p{)}^{25}$Al Reaction Rate Determined at Gamow Energy

Abstract

We report the first (in)elastic scattering measurement of ${}^{25}\mathrm{Al}+p$ with the capability to select and measure in a broad energy range the proton resonances in ${}^{26}$Si contributing to the ${}^{22}$Mg$(\alpha ,p)$ reaction at type I x-ray burst energies. We measured spin-parities of four resonances above the $\alpha$ threshold of ${}^{26}$Si that are found to strongly impact the ${}^{22}$Mg$(\alpha ,p)$ rate. The new rate advances a state-of-the-art model to remarkably reproduce light curves of the GS 1826$-$24 clocked burster with mean deviation $<9$ % and permits us to discover a strong correlation between the He abundance in the accreting envelope of photospheric radius expansion burster and the dominance of ${}^{22}$Mg$(\alpha ,p)$ branch.

Comments: accepted by Physical Review Letters on 5 August 2021, published 19 October 2021