X-ray monitoring of the Wolf-Rayet binary WR140 with Suzaku

摘要

We report on preliminary results of the Suzaku observations of the W-R binary WR 140 (WC7+O5I), with the aim of understanding the W-R stellar wind as well as the wind-wind collision shocks. Our observations, with exposures of 210 ksec in total were made at four different epochs around periastron passage in Jan. 2009. We detected hard X-ray excess in the HXD band. This is the first time that the hard X-ray excess above 10 keV was detected from a W-R binary. Moreover, we found a part of the soft component is not absorbed even by the dense wind. The spectra can be fitted by three different components, with a stationary soft component at kT~0.1 keV, a high temperature component at kT~3 keV and a harder power-low component. The column density at periastron is a factor of 30 higher than that at pre-periastron, which can be explained as self-absorption of the W-R wind. It is found that the emission measure of high temperature component is not proportional to the inverse of the separation of the two stars.