V444 Cyg X-ray and polarimetric variability: Radiative and Coriolis forces shape the wind collision region

TL;DR

This study combines X-ray and polarimetric observations to reveal the 3-D structure and dynamics of the wind collision region in the V444 Cyg binary system, highlighting the effects of radiative and Coriolis forces.

Contribution

It provides the most comprehensive X-ray light curve and polarimetric analysis of V444 Cyg, demonstrating the influence of radiative braking and Coriolis distortion on the wind collision region.

Findings

Detection of Coriolis distortion in X-ray light curves

Large opening angle indicating radiative braking

Polarimetric evidence of wind-wind collision cavity

Abstract

We present results from a study of the eclipsing, colliding-wind binary V444 Cyg that uses a combination of X-ray and optical spectropolarimetric methods to describe the 3-D nature of the shock and wind structure within the system. We have created the most complete X-ray light curve of V444 Cyg to date using 40 ksec of new data from Swift, and 200 ksec of new and archived XMM-Newton observations. In addition, we have characterized the intrinsic, polarimetric phase-dependent behavior of the strongest optical emission lines using data obtained with the University of Wisconsin's Half-Wave Spectropolarimeter. We have detected evidence of the Coriolis distortion of the wind-wind collision in the X-ray regime, which manifests itself through asymmetric behavior around the eclipses in the system's X-ray light curves. The large opening angle of the X-ray emitting region, as well as its location (i.e. the WN wind does not collide with the O star, but rather its wind) are evidence of radiative braking/inhibition occurring within the system. Additionally, the polarimetric results show evidence of the cavity the wind-wind collision region carves out of the Wolf-Rayet star's wind.