Determination of parameters of long-term variability of the X-ray pulsar LMC X-4

Abstract

We have investigated the temporal variability of the X-ray flux measured from the high-mass Xray binary LMCX-4 on time scales from several tens of days to tens of years, i.e., exceeding considerably the orbital period (1.408 days). In particular, we have investigated the 30-day cycle of modulation of the X-ray emission from the source (superorbital or precessional variability) and refined the orbital period and its first derivative. We show that the precession period in the time interval 1991--2015 is near its equilibrium value $P_{sup}=30.370$ days, while the observed historical changes in the phase of this variability can be interpreted in terms of the "red noise" model. We have obtained an analytical law from which the precession phase can be determined to within 5\% in the entire time interval under consideration. Using archival data from several astrophysical observatories, we have found 43 X-ray eclipses in LMC X-4 that, together with the nine eclipses mentioned previously in the literature, have allowed the parameters of the model describing the evolution of the orbital period to be determined. As a result, the rate of change in the orbital period ${\dot{P}}_{orb}/P_{orb}=(1.21\pm 0.07)\times 10^{-6}$ yr${}^{-1}$ has been shown to be higher than has been expected previously.

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• The Swift/BAT Hard X-ray Transient Monitor
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• Cobalt-56 gamma-ray emission lines from the type Ia supernova 2014J

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• Observations of the X-ray pulsar LMC X-4 with NuSTAR: limit on the magnetic field and tomography of the system in the fluorescent iron line
• Broadband mHz QPOs and spectral study of LMC X$-$4 with AstroSat
• Near-periodical spin period evolution in the binary system LMC X-4
• Discovery of pulsation dropout and turn-on during the high state of the accreting X-ray pulsar LMC X-4
• A Study of the 20 Day Superorbital Modulation in the High-Mass X-ray Binary IGR J16493-4348
• Peculiarities of super-Eddington flares from the X-ray pulsar LMC X-4 with NuSTAR
• Discovery of Quasi Periodic Oscillations in the persistent X-ray emission of Accreting Binary X-ray Pulsar LMC X-4
• Disk precession to explain the super-orbital modulation of LMC X-4: results from the Swift monitoring campaign