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

TL;DR

This study measures proton resonances in $^{26}$Si to refine the $^{22}$Mg$( alpha,p)$ reaction rate, significantly improving models of type I X-ray bursts and revealing a correlation between helium abundance and reaction branch dominance.

Contribution

It provides the first elastic scattering measurement of $^{25}$Al+p over a broad energy range, determining key resonances that impact X-ray burst models.

Findings

New $^{22}$Mg$( alpha,p)$ rate improves light curve modeling of X-ray bursters.

Identified resonances strongly influence the reaction rate and burst behavior.

Discovered correlation between helium abundance and reaction branch dominance.

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.