Simulations of stellar winds from X-ray bursts. Characterization of solutions and observable variables

TL;DR

This study models stellar winds during X-ray bursts using updated physics and numerical methods, revealing correlations between observable magnitudes and wind parameters that can inform neutron star properties.

Contribution

It introduces a modern, spherically-symmetric wind model with comprehensive parameter exploration to better understand observable signatures of stellar winds in X-ray bursts.

Findings

Strong correlation between photospheric magnitudes and wind parameters

Photospheric ratio of gravitational energy outflow to radiative luminosity relates to wind velocity

Modeling approach enhances interpretation of neutron star observations

Abstract

Photospheric radius expansion during X-ray bursts can be used to measure neutron star radii and help constrain the equation of state of neutron star matter. Understanding the stellar wind dynamics is important for interpreting observations. Stellar wind models, though studied in past decades, have thus regained interest and need to be revisited with updated data and methods. In this work we study the radiative wind model in the context of XRBs, with modern techniques and physics input. We focus on characterization of the solutions and study of observable magnitudes as a function of free model parameters. We implement a spherically-symmetric non-relativistic wind model in a stationary regime, with updated opacity tables and modern numerical techniques. Total mass and energy outflows $(\dot M,\dot E)$ are treated as free parameters. A high resolution parameter space exploration was performed to allow better characterization of observable magnitudes. High correlation was found between different photospheric magnitudes and free parameters. For instance, the photospheric ratio of gravitational energy outflow to radiative luminosity is in direct proportion to the photospheric wind velocity. The correlations found could help determine the physical conditions of the inner layers, where nuclear reactions take place, by means of observable photospheric values. Further studies are needed to determine the range of physical conditions in which the correlations are valid.