  Geometry and dynamical structure of emission regions in accreting pulsars are
shaped by the interplay between gravity, radiation, and strong magnetic field,
which significantly affects the opacities of a plasma and radiative pressure
under such extreme conditions. Quantitative consideration of magnetic plasma
opacities is, therefore, an essential ingredient of any self-consistent
modeling of emission region structure of X-ray pulsars. We present results of
computations of the Rosseland and Planck mean opacities of a strongly
magnetized plasma with a simple chemical composition,namely the solar
hydrogen/helium mix. We consider all relevant specific opacities of the
magnetized plasma including vacuum polarization effect and contribution of
electron-positron pairs where the pair number density is computed in the
thermodynamic equilibrium approximation. The magnetic Planck mean opacity
determines the radiative cooling of an optically thin strongly magnetized
plasma. It is by factor of three smaller than non-magnetic Planck opacity at
$k_{\rm B}T < 0.1\,E_{\rm cyc}$ and increases by a factor of $10^2 - 10^4$ at
$k_{\rm B}T > 0.3\,E_{\rm cyc}$ due to cyclotron thermal processes. We propose
a simple approximate expression which has sufficient accuracy for the magnetic
Planck opacity description. We provide the Rosseland opacity in a tabular form
computed in the temperature range 1 - 300 keV, magnetic field range $3 \times
10^{10} - 10^{15}$ G, and a broad range of plasma densities. We demonstrate
that the scattering on the electron-positron pairs increases the Rosseland
opacity drastically at temperatures >50 keV in the case of mass densities
typical for accretion channel in X-ray pulsars.
