  The COMPTEL experiment on CGRO observed the gamma-ray sky at energies from
0.75 MeV to 30 MeV between April 1991 and June 2000. COMPTEL detected many
gamma-ray sources, among them an unidentified one labeled GRO J1823-12, which
is positionally consistent with the prominent high-mass X-ray binary LS 5039.
Because LS 5039 was established as gamma-ray emitter during recent years, whose
gamma-radiation radiation is modulated along its binary orbit, we reanalysed
the COMPTEL data of GRO J1823-12 including an orbital resolved analysis. We
find a significant MeV source, showing evidence for a modulated MeV flux
corresponding to the orbital period of LS 5039 of about 3.9 days. We show that
its MeV emission is stronger at the orbital part around the inferior conjuction
than at the part of the superior conjunction, being in phase with X-rays and
TeV gamma-rays, however being in anti-phase with GeV gamma-rays. We conclude
that the COMPTEL source GRO J1823-12 is the counterpart of the microquasar
candidate LS 5039, at least for the majority of its MeV emission. The COMPTEL
fluxes, put into multifrequency perspective, provide new constraints on the
modelling of the high-energy emission of LS 5039.
