Simultaneous radio and X-ray observations of the Wolf-Rayet star WR 147

We present results of simultaneous ASCA/Very Large Array (VLA) observations of the Wolf-Rayet star WR 147 (AS 431). This WN 8 star is an optical doubl e and may be a WR+OB colliding wind binary system. The new observations pla ce tight constraints on the origin of its X-ray and radio emission. The X-r ay emission is due to a multitemperature, optically thin thermal plasma, wi th the dominant contribution coming from plasma at kT approximate to 1 keV. The absorption column density derived from the X-ray spectrum is N-H = 2 x 10(22) cm(-2), which agrees well with estimates based on the visual extinc tion but is too large to explain by wind absorption alone. The X-ray temper ature structure is consistent with colliding wind shock emission, but the u nabsorbed X-ray Luminosity L-x = 10(32.55) ergs s(-1) (0.5-10 keV) is sever al times smaller than that predicted from colliding wind shock models. The VLA data provide the most complete picture ever obtained of the radio spect ral energy distribution of a WR star and consist of near-simultaneous obser vations at five different wavelengths (1.3, 2, 3.6, 6, and 21 cm). The radi o emission consists of a thermal free-free component from the WR wind and a nonthermal component. If the nonthermal emission is due to relativistic pa rticles accelerated by the Fermi mechanism in wind shocks, then the flux is expected to decline at high frequencies according to S-nu proportional to nu(-0.5). However, the observed falloff is much steeper and cannot be repro duced by a simple power law or by synchrotron models that assume power-law electron energy distributions. A surprising result is that the nonthermal e mission can be accurately modeled as synchrotron radiation from relativisti c electrons that are nearly monoergetic.