Paper detail

Unraveling the nature of a deeply embedded Wolf-Rayet star WR 121a

An X-ray study of a deeply embedded Wolf-Rayet star WR 121a has been carried out using long-term (spanning over ~12 years) archival observations from Chandra and XMM-Newton. For the first time, a periodic variation with a period of 4.1 days has been detected in the X-ray light curve of WR 121a. No companion is seen in a merged and exposure corrected Chandra X-ray image of WR 121a as shown in the other previous observations in J-band. The X-ray spectrum of WR 121a has been well-explained by a thermal plasma emission model with temperatures of 0.98+/-0.34 keV and 3.55+/-0.69 keV for the cool and hot components, respectively and non-solar abundances. The present study indicates that WR121a is one of the X-ray bright massive binaries with an X-ray luminosity of ~10^34 erg/s, which can be explained by an active wind collision between its components. The phase-locked modulations have been seen in the flux variation of WR 121a where the flux is increased by a factor of ~1.6 from minimum to maximum in 0.3-10.0 keV energy band. These variations could be caused by an eclipse of the wind collision region by the secondary star in a binary orbit. The winds of both components of WR 121a appear to be radiative. Radiative inhibition as well as radiative braking are the most likely processes those are affecting the wind collision severely in this short period massive binary system.