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We report on the results from Suzaku broadband X-ray observations of thegalactic binary source LS5039. The Suzaku data, which have continuous coverageof more than one orbital period, show strong modulation of the X-ray emissionat the orbital period of this TeV gamma-ray emitting system.The X-ray emissionshows a minimum at orbital phase ~ 0.1, close to the so-called superiorconjunction of the compact object, and a maximum at phase ~0.7, very close tothe inferior conjunction of the compact object. The X-ray spectral data up to70 keV are described by a hard power-law with a phase-dependent photon indexwhich varies within Gamma ~1.45 - 1.61. The amplitude of the flux variation isa factor of 2.5, but is significantly less than that of the factor ~8 variationin the TeV flux. Otherwise the two light curves are similar, but not identical.Although periodic X-ray emission has been found from many galactic binarysystems, the Suzaku result implies a phenomenon different from the "standard"origin of X-rays related to the emission of the hot accretion plasma formedaround the compact companion object. The X-ray radiation of LS5039is likely tobe linked to very-high-energy electrons which are also responsible for the TeVgamma-ray emission. While the gamma-rays are the result of inverse Comptonscattering by electrons on optical stellar photons, X-rays are produced viasynchrotron radiation. Yet, while the modulation of the TeV gamma-ray signalcan be naturally explained by the photon-photon pair production and anisotropicinverse Compton scattering, the observed modulation of synchrotron X-raysrequires an additional process, the most natural one being adiabatic expansionin the radiation production region.

Study of the Spectral and Temporal Characteristics of X-Ray Emission of the Gamma-Ray Binary LS 5039 with Suzaku