Advancement of Photospheric Radius Expansion and Clocked Type-I X-Ray Burst Models with the New Mg22(α,p)

Abstract

We report the first (in)elastic scattering measurement of 25 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(α, p) reaction at type I x-ray burst energies. We measured spin-parities of four resonances above the α threshold of 26 Si that are found to strongly impact the 22 Mg(α, p) rate. The new rate advances a state-ofthe-art model to remarkably reproduce lightcurves 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(α, p) branch.

Impact of the New 65As(p,γ)66Se Reaction Rate on the Two-proton Sequential Capture of 64Ge, Weak GeAs Cycles, and Type I X-Ray Bursts Such as the Clocked Burster GS 1826−24

“…This state-of-the-art GS 1826−24 model was even recently advanced by the newly deduced 22 Mg(α,p) 25 Al reaction rate to match with observation (Hu et al 2021). As the abundances of synthesized isotopes are not observed, we remark here that using a set of high-fidelity XRB models capable of closely reproducing the observed burst light curves is important for us to diagnose the nuclear reaction flow and abundances of synthesized isotopes in the accreted envelope.…”

“…Other models that adopt the same astrophysical settings but implement the Present 65 As(p,γ) 66 Se forward and reverse rate (solid and dotted red lines in the top panel of Figure 5), or the lower limit of Present 65 As(p,γ) 66 Se forward and reverse rates (lower borders of red and pink zones in the top panel of Figure 5), or the Present 65 As(p,γ) 66 Se forward and reverse rate (solid and dotted red lines in the top panel of Figure 5) and 22 Mg(α,p) 25 Al (Hu et al 2021) rates are labeled as the Present † , Present ‡ , and Present § models, respectively. These Present †, ‡, § models take into account the recently updated reaction rates around historical 56 We select the latest 22 Mg(α,p) 25 Al reaction rate, which was experimentally deduced by Hu et al (2021) with the important nuclear structure properties corresponding to the XRB Gamow window instead of the 22 Mg(α,p) 25 Al reaction rate deduced by Randhawa et al (2020) via direct measurement. This is because the Randhawa et al (2020) rate was extrapolated from the non-XRB energy region and may have an additional and large uncertainty that was not shown (Hu et al 2021).…”

“…According to this GS 1826−24 model (Heger et al 2007;Cyburt et al 2016;Jacobs et al 2018;Johnston et al 2020;Hu et al 2021;Lam et al 2022), throughout the course of the XRBs of the GS 1826−24 clocked burster, the nuclear reaction flow has to break out from the ZnGa cycles to reach the GeAsSe region. The reaction flow inevitably goes through the 64 Ge waiting point and also the GeAs cycles that might exist (Van Wormer et al 1994) before surging through the region heavier than the Ge and Se isotopes where hydrogen is intensively burned.…”

“…We then employ the one-dimensional multi-zone hydrodynamic KEPLER code (Weaver et al 1978;Woosley et al 2004;Heger et al 2007) to instantiate XRB simulations that produce a set of XRB episodes matched with the GS 1826−24 clocked burster with the newly deduced 65 As(p,γ) 66 Se forward and reverse reaction rates. Other recently updated reaction rates, i.e., 55 Ni(p,γ) 56 Cu (Valverde et al 2019), 56 Ni(p,γ) 57 Cu (Kahl et al 2019), 57 Cu(p,γ) 58 Zn (Lam et al 2022), and 64 Ge(p,γ) 65 As (Lam et al 2016) around the historic 56 Ni and 64 Ge waiting points, and 22 Mg(α,p) 25 Al (Hu et al 2021) at the important 22 Mg branch point are also taken into account. In Section 3, we study the influence of these 65 As(p,γ) 66 Se forward and reverse rates, and also investigate the influence of the 2p-capture on 64 Ge and GeAs cycles on XRB light curves, on the rp-process path during the thermonuclear runaway of the GS 1826−24 clocked XRBs, and on the nucleosyntheses in and evolution of the accreted envelope along the mass coordinate for nuclei of mass A = 59, ..., 68.…”

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

“…The period of this transient existence may depend on the precise determination of the S p ( 66 Se) value. The Present 57 Cu(p,γ) 58 Zn reaction rate, which is more constrained than Langer et al (2014) reaction rate, was used by Lam et al (2022) to study the weak GeAs cycles and was also recently used by Hu et al (2021) to study the prevailing influence of the newly deduced 22 Mg(α,p) 25 Al.…”