We present XMM-Newton observations of the WC binary \theta Muscae ( WR 48 ) , the second brightest Wolf-Rayet binary in optical wavelengths .
The system consists of a short-period ( 19.1375 days ) WC5/WC6 + O6/O7V binary and possibly has an additional O supergiant companion ( O9.5/B0Iab ) which is optically identified at a separation of \sim 46 mas .
Strong emission lines from highly ionized ions of C , O , Ne , Mg , Si , S , Ar , Ca and Fe are detected .
The spectra are fitted by a multi-temperature thin-thermal plasma model with an interstellar absorption N _ { \mathrm { H } } = 2–3 \times 10 ^ { 21 } \mathrm { cm } ^ { -2 } .
Lack of nitrogen line indicates that the abundance of carbon is at least an order of magnitude larger than that of nitrogen .
A Doppler shift of \sim 630 \mathrm { km } \mathrm { s } ^ { -1 } is detected for the O VIII line , while similar shifts are obtained from the other lines .
The reddening strongly suggests that the emission lines originated from the wind-wind shock zone , where the average velocity is \sim 600 \mathrm { km } \mathrm { s } ^ { -1 } .
The red-shift motion is inconsistent with a scenario in which the X-rays originate from the wind-wind collision zone in the short-period binary , and would be evidence supporting the widely separated O supergiant as a companion .
This may make up the collision zone be lying behind the short-period binary .
In addition to the emission lines , we also detected the RRC ( radiative recombination continuum ) structure from carbon around 0.49 \mathrm { keV } .
This implies the existence of additional cooler plasma .