Study of the ³⁴Ar(α,p)³⁷K reaction rate via proton scattering on ³⁷K, and its impact on properties of modeled X-Ray bursts

Type I X-Ray bursts (XRBs) are extremely energetic stellar explosions that occur on the surface of a neutron star in an accreting binary system with a low mass H/He rich companion.

If accretion reaches a critical fraction of the Eddington luminosity, a thin-shell instability causes a He-flash in the surface nucleosynthesis, resulting in thermonuclear runaway. This is accompanied by a burst of photons in the X-ray spectrum, referred to as a ”light curve”, which has a steep rise preceding the peak, followed by an exponential decay. The rate of the reaction 34Ar(α,p)37K, as one of the last reactions in the so-called (α, p) process that characterize the burst rise, may influence the shape of the light curve, as shown in the most recent XRB sensitivity studies. This work discusses an experiment to study resonances of the 38K compound nucleus of the (α, p) reaction on the 34Ar nucleus via proton scattering on 37K. The experiment was undertaken in 2016 at the National Superconducting Cyclotron Laboratory, using the REA3 re-accelerator, and detector equipment designed and built at Louisiana State University. The kinematics were designed specifically to identify resonances in the Gamow energy window for the temperature regime of the XRB. As the resonant reaction rate is dependent on these levels, this constrains the existing reaction rate. The newly estimated rate is applied to XRB models built using Modules for Experiments in Stellar Astrophysics (MESA), to examine its impact on observables, including the light curve and abundances.