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

TL;DR

This study analyzes long-term X-ray spectral data of the Wolf-Rayet binary WR 102-1, revealing wind distortion effects through observed spectral shifts and absorption variations over multiple years.

Contribution

It provides the first long-term X-ray monitoring of WR 102-1, demonstrating wind distortion evidence via spectral line shifts and absorption changes.

Findings

Detected significant redshifts in iron K-emission lines.

Observed smaller circumstellar absorption during redshift periods.

Suggests wind distortion due to rapid orbital motion.

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 March 2003 and the Suzaku observation in September 2006. Furthermore, when the red-shift 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.