RXTE, Swift & NICER obs. of WR 140

Bright, variable X-ray emission is generated in shocks produced by the collision of the winds of the WC7pd+O5.5fc component stars. We discuss the variations in the context of the colliding-wind model using broadband spectrometry from the RXTE, Swift, and NICER observatories obtained over 20yr and nearly 1000 observations through three consecutive 7.94yr orbits, including three periastron passages.

The X-ray luminosity varies as expected with the inverse of the stellar separation over most of the orbit; departures near periastron are produced when cooling shifts to excess optical emission in CIII{lambda}5696 in particular. We use X-ray absorption to estimate mass-loss rates for both stars and to constrain the system morphology. The absorption maximum coincides closely with the inferior conjunction of the WC star and provides evidence of the ion-reflection mechanism that underlies the formation of collisionless shocks governed by magnetic fields probably generated by the Weibel instability.