Hydrodynamic and radiative transfer modeling of X-ray emission from colliding WR winds: WR 140 & the Galactic center

TL;DR

This study models X-ray emissions from colliding Wolf-Rayet star winds using 3D hydrodynamic and radiative transfer simulations, successfully matching observations of WR 140 and the Galactic center in key aspects.

Contribution

It introduces detailed 3D hydrodynamic and radiative transfer models to simulate X-ray emissions from WR star wind collisions, improving understanding of these complex systems.

Findings

Model reproduces WR 140 X-ray light curve well except at periastron.

Simulated spectra match observed hardness ratios and spectral shapes.

Galactic center model aligns with Chandra data within 3 arcseconds but declines too rapidly beyond.

Abstract

Colliding Wolf-Rayet (WR) winds produce thermal X-ray emission widely observed by X-ray telescopes. In wide WR+O binaries, such as WR 140, the X-ray flux is tied to the orbital phase, and is a direct probe of the winds' properties. In the Galactic center, $\sim$30 WRs orbit the super massive black hole (SMBH) within $\sim$10", leading to a smorgasbord of wind-wind collisions. To model the X-ray emission of WR 140 and the Galactic center, we perform 3D hydrodynamic simulations to trace the complex gaseous flows, and then carry out 3D radiative transfer calculations to compute the variable X-ray spectra. The model WR 140 RXTE light curve matches the data well for all phases except the X-ray minimum associated with periastron, while the model spectra agree with the RXTE hardness ratio and the shape of the Suzaku observations throughout the orbit. The Galactic center model of the Chandra flux and spectral shape match well in the region r$<$3", but the model flux falls off too rapidly beyond this radius.