Dependence of X-Ray Burst Models on Nuclear Reaction Rates

Abstract

X-ray bursts are thermonuclear flashes on the surface of accreting neutron stars and reliable burst models are needed to interpret observations in terms of properties of the neutron star and the binary system. We investigate the dependence of X-ray burst models on uncertainties in (p,γ), (α,γ), and (α,p) nuclear reaction rates using fully self-consistent burst models that account for the feedbacks between changes in nuclear energy generation and changes in astrophysical conditions. A two-step approach first identified sensitive nuclear reaction rates in a single-zone model with ignition conditions chosen to match calculations with a state-of-the-art 1D multi-zone model based on the Kepler stellar evolution code. All relevant reaction rates on neutron deficient isotopes up to mass 106 were individually varied by a factor of 100 up and down. Calculations of the 84 highest impact reaction rate changes were then repeated in the 1D multi-zone model. We find a number of uncertain reaction rates that affect predictions of light curves and burst ashes significantly. The results provide insights into the nuclear processes that shape X-ray burst observables and guidance for future nuclear physics work to reduce nuclear uncertainties in X-ray burst models.

New Reaction Rates Of 64Ge(p,γ)65As(p,γ)66Se And The Impact On Type I X-ray Bursts

“…The last two models are fully self-consistent that consider the mutual influence of changes between nuclear energy generation and astrophysical condition [20]. However, there is no direct measurement of these two reactions at the respective energy range in XRBs.…”

“…In recent reviews of XRB models [5,6,17,18,19], including post-processing model [18], onezone model [15,17], and multizone 1D hydrodynamic model [20], the reactions of 64 Ge(p,γ) 65 As and 65 As(p,γ) 66 Se are identified to have a critical impact on nucleosynthesis during XRBs. The last two models are fully self-consistent that consider the mutual influence of changes between nuclear energy generation and astrophysical condition [20].…”

Constraining astrophysical reaction rates: using the storage rings at FAIR/GSI

“…An important branching point is identified at the radioactive 59 Cu isotope. It has been shown recently, that the (p, γ) -(p, α) branching on 59 Cu determines the breakout out of the important 56 Ni waiting point [5,6], see left part of Fig. 3.…”

Studies of X-ray burst reactions with radioactive ion beams from RESOLUT

“…see [2]) are providing insights into the composition, dynamics, and evolution of these systems. Simulations also show that certain nuclear reactions involving proton-rich, radioactive nuclei have a direct impact on energy generation, nucleosynthesis, and the resulting light curve [3,4]. The rates of many of these reactions are purely theoretical or have large uncertainties due to experimental challenges in studying short-lived nuclei that hinder our understanding of X-ray bursts.…”