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Researchers analyzing 157 months of hard X-ray data from the X-ray binary system GX 301-2 have detected an unusual dual-superorbital modulation pattern, with a primary 115-day cycle and a weaker 65-day cycle. Using multiple timing analysis methods, they determined that the 115-day period represents the true superorbital modulation while the 65-day signal is likely a beat frequency resulting from interaction with the system's orbital period. The findings suggest these modulations originate from corotating interaction regions in the stellar wind, though the underlying physical mechanism remains incompletely understood.
Why it matters
This discovery advances understanding of wind-fed X-ray binary systems and the complex interactions between stellar winds and compact objects. The identification of dual-modulation behavior and its potential connection to corotating interaction regions provides observational constraints for theoretical models of these high-energy astrophysical systems.
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⚠️ Preprint – Noch nicht peer-reviewed
Dieser Artikel wurde noch nicht von unabhängigen Experten begutachtet. Die Ergebnisse sind vorläufig und sollten mit Vorsicht interpretiert werden.
Abstract: The superorbital modulations (SMs) observed in wind-fed X-ray binaries remain a puzzling phenomenon in astrophysics. To investigate this behavior observationally, we analyzed the long-term hard X-ray light curve from the Swift/BAT 157-Month Hard X-ray Survey in X-ray binary GX 301-2. Using three timing analysis methods–the Lomb-Scargle periodogram, the weighted wavelet Ztransform, and Gaussian processes–we identify a rare dual-SM behavior in this source: the 115-day modulation exceeds the 5$sigma$ global significance level, whereas the 65-day signal only marginally reaches the 4$sigma$ level. Because the 115-day period is more consistent with the previously reported linear relation between orbital and superorbital periods, we interpret 115 days as the actual superorbital period, while the weaker and less stable 65-day period is its beat modulation with the orbital period.By assessing the applicability of different physical scenarios to our results, we suggest that this dual-SM behavior is most plausibly associated with corotating interaction regions (CIRs) in the stellar wind. This framework can also account for the observed linear orbital-superorbital relation, despite the unclear physical mechanism that sets the apparent ratio between the CIR and orbital periods across sources. Further long-term monitoring of this system, together with continued theoretical development of the CIR scenario, will be essential for clarifying the origin of wind-fed SMs.
Source: Detection of a puzzling dual-superorbital hard X-ray modulation in the X-ray binary GX 301-2