The variable X-ray spectrum of theWolf-Rayet binary WR140 with Suzaku
Department of Physics, Chuo University, Japan
Department of High Energy Astrophysics, ISAS/JAXA
Department of Physics, Chuo University, Japan
CRESST and X-ray Astrophysics Laboratory NASA/GSFC, and
Department of Physics, University of Maryland
CRESST and X-ray Astrophysics Laboratory NASA/GSFC, and
Universities Space Research Association
European Space Agency, XMM-Newton Science Operations Centre
Département de Physique, Université de Montréal
Institute for Astronomy, Royal Observatory Edinburgh
Abstract
We report the preliminary results of the Suzaku observations of the W-R binaryWR140 (WC7+O5I). We executed the observations at four different epochs around periastron passage in Jan. 2009 to understand the W-R stellar wind as well as the wind-wind collision shocks. The total exposure was 210 ks. We detected hard X-ray excess in the HXD band (> 10 keV) for the first time from a W-R binary. Another notable discovery was a soft component which is less absorbed even by the dense wind. The spectra can be fitted by three different components; one is for the cool component with kT=0.1–0.6 keV, one for a dominant high-temperature component with kT ~3 keV, and one for the hardest power-law component with the photon index of ~2. As periastron approached, the column density of the high-temperature component increased, which can be explained as self-absorption by the W-R wind. The emission measure of the dominant, high-temperature component is not inversely proportional to the distance between the two stars.