Modeling X-ray Bursting Neutron Star Atmospheres

Abstract

We present a verification of a computational model, developed at the Los Alamos National Laboratory (LANL) for simulating radiation transfer in X-ray bursting neutron star atmospheres. We tested a baseline case and demonstrated strong agreement in the behavior of the outgoing spectrum's color-correction factor with earlier work and theoretical expectations. By analyzing the relationship between the simulation time and outgoing flux, we also demonstrated how the model calculates through a sequence of time-independent atmospheric snapshots, each iteratively refined, and uses them to progressively converge toward the correct atmospheric state (as would be observed during a burst). We examined the behavior of the outgoing flux across different optical depths and explored the physical explanations for deviations from a pure blackbody spectrum, attributed to frequency-dependent opacity sources. Additionally, we assessed the impact of Compton scattering, highlighting its role in redistributing photon energies.