The X-ray light curve of the massive colliding wind Wolf-Rayet + O binary WR21a

Abstract

Our dedicated XMM-Newton monitoring, as well as archival Chandra and Swift datasets, were used to examine the behaviour of the WN5h+O3V binary WR21a at high energies. For most of the orbit, the X-ray emission exhibits few variations. However, an increase in strength of the emission is seen before periastron, following a 1/D relative trend, where D is the separation between both components. This increase is rapidly followed by a decline due to strong absorption as the Wolf-Rayet (WR) comes in front. The fitted local absorption value appears to be coherent with a mass-loss rate of about 1x10^{-5} M_sol/yr for the WR component. However, absorption is not the only parameter affecting the X-ray emission at periastron as even the hard X-ray emission decreases, suggesting a possible collapse of the colliding wind region near to or onto the photosphere of the companion just before or at periastron. An eclipse may appear as another potential scenario, but it would be in apparent contradiction with several lines of evidence, notably the width of the dip in the X-ray light curve and the absence of variations in the UV light curve. Afterwards, the emission slowly recovers, with a strong hysteresis effect. The observed behaviour is compatible with predictions from general wind-wind collision models although the absorption increase is too shallow.

Accepted for publication in Astronomy & Astrophysics

References in corpus (10)

• The Galactic WN stars: Spectral analyses with line-blanketed model atmospheres versus stellar evolution models with and without rotation
• Mass loss from late-type WN stars and its Z-dependence: very massive stars approaching the Eddington limit
• An XMM-Newton view of the young open cluster NGC 6231 -- II. The OB star population
• Spatial distribution of Galactic Wolf-Rayet stars and implications for the global population
• Fermi-LAT Search for Pulsar Wind Nebulae around gamma-ray Pulsars
• Chandra monitoring of the very massive binary WR20a and the young massive cluster Westerlund2
• The mass of the very massive binary WR21a
• The very massive X-ray bright binary system Wack 2134 (= WR 21a)
• V444 Cyg X-ray and polarimetric variability: Radiative and Coriolis forces shape the wind collision region
• Phase-resolved XMM-Newton and swift observations of WR 25

Cited by in corpus (18)

• Colliding Stellar Winds Structure and X-ray Emission
• The Massive Star-Forming Regions Omnibus X-Ray Catalog, Third Installment
• The X-ray emission of Be+stripped star binaries
• The 155-day X-ray cycle of the very massive Wolf-Rayet star Melnick 34 in the Large Magellanic Cloud
• A modern study of HD166734: a massive supergiant system
• A changing wind collision
• Long-term soft and hard X-ray investigation of the colliding wind WN+O binary WR 25
• New X-ray detections of known Wolf-Rayet stars
• Variations on a theme -- the puzzling behaviour of Schulte 12
• Modeling the Optical to Ultraviolet Polarimetric Variability from Thomson Scattering in Colliding Wind Binaries
• The winking eye of a very massive star: WR 21a revealed as an eclipsing binary by TESS
• An X-ray view of HD166734, a massive supergiant system
• X-ray emission of massive stars and their winds
• Discovery of extraordinary X-ray emission from magnetospheric interaction in the unique binary stellar system $\epsilon$ Lupi
• Long-term X-ray variation of the colliding wind Wolf-Rayet binary WR 125
• An X-ray Study of Two B+B Binaries: AH Cep and CW Cep
• Quest for the tertiary component in Cyg OB2 #5
• Perspectives for observing hot massive stars with XMM-Newton in the years 2017 -- 2027