Long-term Stability of Non-thermal X-ray Modulation in the Gamma-ray Binary LS 5039

Abstract

We report on long-term stability of X-ray modulation apparently synchronized with an orbital period of 3.9 days in the gamma-ray binary LS 5039. Recent observations with the Suzaku satellite in the year 2007, which covered continuously more than one orbital period, have provided us with detailed characterization of X-ray flux and spectral shape as a function of orbital phase. Motivated by the results from Suzaku, we have re-analyzed the X-ray data obtained with ASCA, XMM-Newton, and Chandra between 1999 and 2005, to investigate long-term behavior of LS 5039 in the X-ray band. We found that the modulation curves in 1999--2007 are surprisingly stable. Even fine structures in the light curves such as spikes and dips are found to be quite similar from one orbit to another. The spectral characteristics observed in the past are consistent with those seen with Suzaku for some orbital phase segments. We suggest that magneto-hydrodynamical collisions between the relativistic outflow from a compact object and the stellar wind from the O star explain the clock-like non-thermal X-ray emission over eight years through remarkably stable production of high-energy particles near the binary system.

5 pages, 2 figures, accepted in ApJ Letters

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• The gamma-ray binary LS 5039: mass and orbit constraints from MOST observations
• Sign of hard X-ray pulsation from the gamma-ray binary system LS 5039
• VERITAS Observations of the TeV Binary LS I +61 303 During 2008-2010
• Thermal X-ray Emission from the Shocked Stellar Wind of Pulsar Gamma-ray Binaries
• Deep Chandra observations of TeV binaries I: LSI +61 303
• Physical properties of the gamma-ray binary LS 5039 through low and high frequency radio observations
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• Modelling Jets, Tori and Flares in Pulsar Wind Nebulae
• Direct Wind Accretion and Jet Launch in Binary Systems
• Multiwavelength Astronomy and CTA: X-rays
• NuSTAR observation of LS 5039
• Deep Chandra observations of TeV binaries II: LS 5039
• Long-term X-ray monitoring of LS I +61 303: analysis of spectral variability and flares
• X-ray absorption and occultation in LS 5039
• Extended X-ray emission in the vicinity of the microquasar LS 5039: pulsar wind nebula?
• The TeV binary HESS J0632+057 in the low and high X-ray state
• The missing GeV γ-ray binary: Searching for HESS J0632+057 with Fermi-LAT
• Swift observations of 1FGL J1018.6-5856
• Non-thermal radiation from a pulsar wind interacting with an inhomogeneous stellar wind
• Discovery of X-ray Emission from the Galactic Supernova Remnant G32.8-0.1 with Suzaku
• Spectral analysis in orbital/superorbital phase space and hints of superorbital variability in the hard X-rays of LS I +61 303
• The orbital parameters of the gamma-ray binary LMC P3
• Chandra Imaging of Gamma-Ray Binaries
• Broad-Band High-Energy Emission of the Gamma-ray Binary System LS 5039: Spectral and Temporal Features using NuSTAR and Fermi Observations
• NuSTAR Hard X-ray Observation of the Gamma-ray Binary Candidate HESS J1832-093
• Phase-resolved hard X-ray emission of the high-mass binary LS 5039: a spectral hardening above 50 keV detected with INTEGRAL
• Unveiling properties of the non-thermal X-ray production in the gamma-ray binary LS 5039 using the long-term pattern of its fast X-ray variability
• The Supernova Remnant G284.3$-$1.8 and Its Relation to the Gamma-ray Binary 1FGL J1018.6$-$5856