  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.
