  Cygnus X-1 and LS 5039 are two X-ray binaries observed at TeV energies. Both
sources are compact systems, contain jet-like (radio) structures, and harbor
very luminous O stars. A TeV signal has been found around the superior
conjunction of the compact object in both objects, when the highest gamma-ray
opacities are expected. We investigate the implications of finding TeV emission
from Cygnus X-1 and LS 5039 around the superior conjunction, since this can
give information on the system magnetic field and the location of the TeV
emitter. Using the very high-energy spectra and fluxes observed around the
superior conjunction in Cygnus X-1 and LS 5039, we compute the absorbed
luminosity that is caused by pair creation in the stellar photon field for
different emitter positions with respect to the star and the observer line of
sight. The role of the magnetic field and electromagnetic cascading are
discussed. For the case of inefficient electromagnetic cascading, the expected
secondary synchrotron fluxes are compared with the observed ones at X-ray
energies. We find that, in Cygnus X-1 and LS 5039, either the magnetic field in
the star surroundings is much smaller than the one expected for O stars or the
TeV emitter is located at a distance >10^12 cm from the compact object. Our
results strongly suggest that the TeV emitters in Cygnus X-1 and LS 5039 are
located at the borders of the binary system and well above the orbital plane.
This would not agree with those models for which the emitter is well inside the
system, like the innermost-jet region (Cygnus X-1 and LS 5039; microquasar
scenario), or the region between the pulsar and the primary star (LS 5039;
standard pulsar scenario).
