Consistent Modeling of GS 1826-24 X-ray Bursts for Multiple Accretion Rates Demonstrates the Possibility to Constrain rp-process Reaction Rates

TL;DR

This study uses multi-epoch modeling of X-ray bursts from GS 1826-24 with the MESA code to constrain accretion rates, shallow heating, and rp-process reaction rates, demonstrating the potential of light curve analysis for nuclear physics insights.

Contribution

It presents the first comprehensive multi-epoch model comparison for X-ray bursts, enabling constraints on accretion rates, shallow heating, and rp-process reaction rates.

Findings

Accretion rate $\dot{M}$ is higher than previously estimated.

Shallow heating must be below 0.5 MeV/u.

Light curve features can constrain nuclear reaction rates.

Abstract

Type-I X-ray burst light curves encode unique information about the structure of accreting neutron stars and the nuclear reaction rates of the rp-process that powers bursts. Using the first model calculations of hydrogen/helium burning bursts for a large range of astrophysical conditions performed with the code MESA, this work shows that simultaneous model-observation comparisons for bursts from several accretion rates $\dot{M}$ are required to remove degeneracies in astrophysical conditions that otherwise reproduce bursts for a single $\dot{M}$ and that such consistent multi-epoch modeling could possibly limit the $^{15}\rm{O}(\alpha,\gamma)^{19}\rm{Ne}$ reaction rate. Comparisons to the year 1998, 2000, and 2007 bursting epochs of the neutron star GS 1826-24 show that $\dot{M}$ must be larger than previously inferred and that the shallow heating in this source must be below 0.5 MeV/u, providing a new method to constrain the shallow heating mechanism in the outer layers of accreting neutron stars. Features of the light curve rise are used to demonstrate that a lower-limit could likely be placed on the $^{15}\rm{O}(\alpha,\gamma)$ reaction rate, demonstrating the possibility of constraining nuclear reaction rates with X-ray burst light curves.