Exploring the connection between the stellar wind and the non-thermal emission in LS 5039

Abstract

LS 5039 has been observed with several X-ray instruments so far. The source presents X-ray variability at orbital timescales in flux and photon index. The system harbors an O-type main sequence star with moderate mass loss. At present, the link between the X-rays and the stellar wind is unclear. New XMM-Newton observations have been performed around periastron and apastron passages in September 2005, when the stellar wind activity was apparently higher. April 2005 Chandra observations on LS 5039 are also revisited. Moreover, a compilation of Halpha EW data obtained since 1992, from which the stellar mass loss evolution can be approximately inferred, is carried out. XMM-Newton observations show higher and harder emission around apastron than around periastron. No signatures of thermal emission or a reflection iron line indicating the presence of an accretion disk are found in the spectrum, and the hydrogen column density (NH) is compatible with being the same in both observations and consistent with the interstellar value. 2005 Chandra observations show a hard X-ray spectrum, and possibly high fluxes. The Halpha EW shows yearly variations of a ~ 10%, and does not seem to be correlated with X-ray fluxes obtained at similar phases, unlike it would be expected in the wind accretion scenario. 2005 XMM-Newton and Chandra observations are consistent with 2003 RXTE/PCA results. The constancy of the NH seems to imply that either the X-ray emitter is located at >~ 1012 cm from the compact object, or the real N_H is 3-27 times smaller than the one predicted by a spherical symmetric wind model. We suggest that the multiwavelength non-thermal emission of LS 5039 is related to the radio jets and unlikely produced inside the binary system.

7 pages, 3 figures, 3 Tables, accepted for publication in A&A (short abstract version, see abstract paper!), Table 2 will only appear on-line in the journal

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• Thermal X-ray Emission from the Shocked Stellar Wind of Pulsar Gamma-ray Binaries
• Periodic morphological changes in the radio structure of the gamma-ray binary LS 5039
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• Deep Chandra observations of TeV binaries I: LSI +61 303
• Modelling Jets, Tori and Flares in Pulsar Wind Nebulae
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• A Radio Pulsar Search of the Gamma-ray Binaries LS I +61 303 and LS 5039
• Radio continuum and near-infrared study of the MGRO J2019+37 region
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• A dynamical and radiation semi-analytical model of pulsar-star colliding winds along the orbit: Application to LS 5039
• Radio absorption in high-mass gamma-ray binaries
• Monte-Carlo Simulations of Radio Emitting Secondaries in Gamma-Ray Binaries
• Studying the properties of the radio emitter in LS 5039
• Properties of a hypothetical cold pulsar wind in LS~5039
• Gamma-ray binaries beyond one-zone models: an application to LS 5039
• 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
• Low frequency radio spectrum of LS 5039 during periastron and apastron passages
• Looking into the heart of a beast: the black hole binary LS 5039
• On the X-ray/TeV connection in Galactic jet sources