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

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.