We study theoretical interpretations of the 150-d (superorbital) modulation
observed in X-ray and radio emission of Cyg X-1 in the framework of models
connecting this phenomenon to precession. Precession changes the orientation of
the emission source (either disc or jet) relative to the observer. This leads
to emission modulation due to an anisotropic emission pattern of the source or
orientation-dependent amount of absorbing medium along the line of sight or
both. We consider, in particular, anisotropy patterns of blackbody-type
emission, thermal Comptonization in slab geometry, jet/outflow beaming, and
absorption in a coronal-type medium above the disc. We then fit these models to
the data from the RXTE/ASM, CGRO/BATSE, and the Ryle and Green Bank radio
telescopes, and find relatively small best-fit angles between the precession
and orbital planes, ~10-20 degrees. The thermal Comptonization model for the
X-ray emission explains well the observed decrease of the variability amplitude
from 1 to 300 keV as a result of a reduced anisotropy of the emission due to
multiple scatterings. Our modeling also yield the jet bulk velocity of
~(0.3-0.5)c, which is in agreement with the previous constraint from the lack
of an observed counterjet and lack of short-term X-ray/radio correlations.Comment: 10 pages, 9 figures and 2 tables, accepted to MNRA