Influence of Nuclear Reaction Rate Uncertainties on Neutron Star Properties Extracted From X-ray Burst Model-Observation Comparisons

Abstract: Type-I X-ray bursts can be used to determine properties of accreting neutron stars via comparisons between model calculations and astronomical observations, exploiting the sensitivity of models to astrophysical conditions. However, the sensitivity of models to nuclear physics uncertainties calls into question the fidelity of constraints derived in this way. Using X-ray burst model calculations performed with the code {\tt MESA}, we investigate the impact of uncertainties for nuclear reaction rates previously identified as influential and compare them to the impact of changes in astrophysical conditions, using the conditions that are thought to best reproduce the source GS 1826-24 as a baseline. We find that reaction rate uncertainties are unlikely to significantly change conclusions about the properties of accretion onto the neutron star surface for this source. However, we find that reaction rate uncertainties significantly hinder the possibility of extracting the neutron star mass-radius ratio by matching the modeled and observed light curves due to the influence of reaction rates on the modeled light curve shape. Particularly influential nuclear reaction rates are $^{15}{\rm O}(\alpha,\gamma)$ and $^{23}{\rm Al}(p,\gamma)$, though other notable impacts arise from $^{14}{\rm O}(\alpha,p)$, $^{18}{\rm Ne}(\alpha,p)$, $^{22}{\rm Mg}(\alpha,p)$, $^{24}{\rm Mg}(\alpha,\gamma)$, $^{59}{\rm Cu}(p,\gamma)$, and $^{61}{\rm Ga}(p,\gamma)$. Furthermore, we find that varying some nuclear reaction rates within their uncertainties has an impact on the neutron star crust composition and thermal structure that is comparable to relatively significant changes accretion conditions.