Phase-resolved XMM-Newton and swift observations of WR 25

Abstract

We present an analysis of long-term X-ray and optical observations of the Wolf-Rayet binary WR 25. Using archival data from observations with the XMM-Newton and the Swift observatories spanning over ~10 yr, we show that WR 25 is a periodic variable in X-rays with a period of $208\pm 3$ days. X-ray light curves in the 0.5-10.0 keV energy band show phase-locked variability, where the flux increased by a factor of ~2 from minimum to maximum, being maximum near periastron passage. The light curve in the soft energy band (0.5-2.0 keV) shows two minima indicating the presence of two eclipses. However, the light curve in the hard energy band (2.0-10.0 keV) shows only one minimum during the apastron passage. The X-ray spectra of WR 25 were explained by a two-temperature plasma model. Both the cool and the hot plasmas were constant at 0.628+/-0.008 and 2.75+/-0.06 keV throughout an orbital cycle, where the cooler plasma could be due to the small scale shocks in a radiation-driven outflow and the high temperature plasma could be due to the collision of winds. The column density varied with the orbital phase and was found to be maximum after the periastron passage, when the WN star is in front of the O star. The abundances of WR 25 were found to be non-solar. Optical V-band data of WR 25 also show the phase-locked variability, being at maximum near periastron passage. The results based on the present analysis indicate that WR 25 is a colliding wind binary where the presence of soft X-rays is attributed to individual components; however, hard X-rays are due to the collision of winds.

12 pages, 7 figures, 5 tables, ApJ

References in corpus (7)

• Physical Properties of Wolf-Rayet Stars
• The death of massive stars - I. Observational constraints on the progenitors of type II-P supernovae
• The Galactic WN stars: Spectral analyses with line-blanketed model atmospheres versus stellar evolution models with and without rotation
• An XMM-Newton view of the young open cluster NGC 6231 -- II. The OB star population
• XMM-Newton X-ray Observations of the Wolf-Rayet Binary System WR 147
• Neon Abundances from a Spitzer/IRS Survey of Wolf-Rayet Stars
• The X-ray Lightcurve of WR 140

Cited by in corpus (3)

• The Galactic WN stars revisited. Impact of Gaia distances on fundamental stellar parameters
• The variability of the BRITE-est Wolf-Rayet binary, ${\gamma }^2$ Velorum I. Photometric and spectroscopic evidence for colliding winds
• Long-term soft and hard X-ray investigation of the colliding wind WN+O binary WR 25