Long-term X-ray spectral variation of the Wolf–Rayet binary WR 102-1 in the Galactic bulge: evidence for wind distortion in the binary

Abstract

ABSTRACT WR 102-1 was detected by Suzaku as a conspicuous point source in the 6.7 keV intensity map of the central region of the Milky Way. The source was suggested as a possible Wolf–Rayet binary based on its X-ray and infrared spectral characteristics. The iron line emission is expected to originate in the Wolf–Rayet star’s dynamic stellar wind when colliding the companion’s mild stellar wind. Here, we report the result of a long-term X-ray monitoring of WR 102-1 since 1998 using archival data of ASCA, XMM–Newton, Chandra, Suzaku, and Swift to reveal variations of the iron K-emission line and the circumstellar absorption. Consequently, we have detected significant redshifts of the iron K-emission line from the XMM–Newton observation in 2003 March and the Suzaku observation in 2006 September. Furthermore, when the redshift was observed, which suggests that the Wolf–Rayet star was in front of the companion star, the circumstellar absorption values were smaller than other periods. These results appear contrary to the expectation if the Wolf–Rayet’s stellar wind is spherically symmetric, but may be understood if the Wolf–Rayet star’s stellar wind is significantly distorted due to the rapid orbital motion near the periastron.