XMM-Newton & Swift Phase-folded light curve of WR 25
The X-ray light curves as observed from XMM-Newton (MOS) and Swift (XRT) in the total (0.5 - 10.0 keV), hard (2.0 - 10.0 keV) and soft (0.5 - 2.0 keV) energy bands were folded using the ephemeris HJD = 2,451,958.0 + 207.85E (Gamen et al. 2006) and are shown in Figures (a) and (b), respectively. The zero phase in the folded light curves corresponds to the time of periastron (HJD 2,451,958.0). X-ray light curves in each band from both observations show similar behavior. The light curves in the individual bands show phase-locked variability. In the soft- and total-band light curves, the count rates decrease when going from orbital phase 0.0 (i.e., near the periastron passage) to orbital phase ∼0.03, then increase up to phase ∼0.2. Count rates further decrease to phase ∼0.7 before reaching a maximum value near periastron passage. However, in the hard band, the count rates were systematically decreasing when going from periastron to apastron. The ratio of maximum to minimum count rates in total, soft, and hard bands were found to be 1.9, 2.6, and 1.7 for XMM-Newton-MOS observations, and 2.5, 2.6, and 2.9 for Swift-XRT observations, respectively.
[Image Credit: Pandey, Pandey, & Karmakar et al. (2014)]