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arXiv · 1906.00751

Long-term soft and hard X-ray investigation of the colliding wind WN+O binary WR 25

Bharti Arora·J. C. Pandey·M. De Becker
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Abstract

We investigated the long-term behaviour in X-rays of the colliding wind binary WR 25, using archival data obtained with Suzaku, Swift, XMM-Newton, and NuSTAR spanning over ~16 years. Our analysis reveals phase-locked variations repeating consistently over many consecutive orbits, in agreement with an X-ray emission fully explained by thermal emission from the colliding winds in the 208-d orbit. We report on a significant deviation of the X-ray flux with respect to the 1/D trend (expected for adiabatic shocked winds) close to periastron passage. The absence of a drop in post-shock plasma temperature close to periastron suggests this break in trend cannot be explained in terms of reduced pre-shock velocities in this part of the orbit. Finally, NuSTAR data reveal a lack of hard X-ray emission (above 10.0 keV) above the background level. Upper limits on a putative non-thermal emission strongly suggest that the sensitivity of present hard X-ray observatories is not sufficient to detect non-thermal emission from massive binaries above 10 keV, unless the wind kinetic power is large enough to significantly feed particle acceleration in the wind-wind interaction.

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Bharti Arora, J. C. Pandey, M. De Becker. 2019-05-31. Long-term soft and hard X-ray investigation of the colliding wind WN+O binary WR 25. https://doi.org/10.1093/mnras/stz1447

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