3D Dynamical Modeling of Wind Accretion in Cyg X-3

TL;DR

This study uses 3D hydrodynamic simulations to explore wind accretion in Cyg X-3, revealing complex flow structures influenced by rapid orbital motion and providing insights into accretion rates and X-ray emission patterns.

Contribution

It presents the first detailed 3D hydrodynamic modeling of wind accretion in Cyg X-3, highlighting the effects of orbital motion on flow structure and accretion rates.

Findings

Accretion rate is lower than Bondi-Hoyle-Lyttleton estimate.

Flow around the compact object exhibits large density gradients.

Model X-ray light curve roughly matches observations.

Abstract

Cyg X-3 is a high mass X-ray binary consisting of a Wolf-Rayet star and a compact object in a very short orbital period of 4.8h. The only confirmed microquasar with high energy gamma-ray emission, Cyg X-3 provides a unique opportunity to study the relationship between the accretion power and the power in high energy emission. Because of a compact orbit and a slow Wolf-Rayet wind, the flow structure around the compact object is thought to be strongly affected by the orbital motion, details of which can be obtained only by numerical simulations. In this paper, we report on the results from 3D hydrodynamic simulations of the wind accretion in Cyg X-3. For simplicity we adopt an anti-gravity-like force that emulates the radiative acceleration consistent with the beta-velocity wind. Due to the rapid orbital motion, the flow around the compact object has large density gradients. As a result, the accretion rate onto the compact object is significantly lower than that of the Bondi-Hoyle-Lyttleton rate. We also calculate the model X-ray light curve. Although it roughly agrees with the observed light curve, more detailed modeling is needed for detailed comparison.