Time-dependent X-ray observations of Wolf-Rayet binaries with O-type and with suspected compact companions

Each of four WR binaries has been observed in the 0.1-5 keV range of four consecutive days for a total of approximately 104 sec with the IPC on the Einstein Observatory. One of the stars is the well-known WN5 + O6 binary V444 Cyg; the other three have suspected compact companions; all have periods close to four days. Neither HD 197406 (WN7) nor HD 96548 (WN8) was detected; hence Lsub(x) (0.5-3.0 keV) < or approximately equal to 1032 erg s-1, which is on the low side, even for O-stars. EZ CMa (WN5) and V444 Cyg are moderately strong, variable X-ray sources with Lsub(x) (0.5-3.0 keV) approximately equal to 1033 erg s-1, kT approximately equal to 0.5 keV and Nsub(H) approximately equal to 1022 cm-2. These values suggest that the X-ray flux arises in the outer part of the wind. The variable component may be produced by collision of two winds. There is no evidence of harder X-rays coming from accretion onto a compact star. Nevertheless, the presence of a collapsar is not excluded at hγ < or approximately equal to 5 keV, where absorption in the WR wind would likely reduce the X-ray flux to a level which is masked by the flux coming from the hot stellar wind. (Auth.)