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