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

¹ Département AGO, Université de Liège, Allée du 6 Août 17, Bât. B5C, 4000 Liège, Belgium
e-mail: Jamie.R.Lomax@ou.edu, naze@astro.ulg.ac.be
² Department of Physics & Astronomy, University of Denver, 2112 E. Wesley Ave., Denver, CO 80210, USA
³ Homer L. Dodge Department of Physics & Astronomy, University of Oklahoma, 440 W Brooks Street, Norman, OK 73019, USA
⁴ Faculty of Engineering, Hokkai-Gakuen University, Toyohira-ku, 062-8605 Sapporo, Japan
⁵ CRESST/NASA Goddard Space Flight Center, Code 662, Greenbelt, MD, 20771; University Space Research Association, Columbia, MD, USA
⁶ Department of Physics & Astronomy, University of Toledo, 2801 W Bancroft St, Toledo, OH 43606, USA
⁷ Department of Physics & Astronomy, East Tennessee State University, Box 70652, Johnson City, TN 37614, USA
⁸ Department of Physics & Astronomy, University of Delaware, Newark, DE 19716, USA
⁹ School of Physics & Astronomy, The University of Leeds, Leeds, LS2 9JT, UK
¹⁰ European Space Agency, XMM-Newton SOC, ESAC, Apartado 78, 28691 Villanueva de la Cañada, Madrid, Spain

Received: 24 June 2014
Accepted: 16 October 2014

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 3D 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 ks of new data from Swift, and 200 ks 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.