VACUUM POLARIZATION EFFECTS ON RADIATIVE OPACITIES IN A STRONG MAGNETIC-FIELD

We study the electromagnetic properties of plasmas allowing for the polarization effect of the vacuum induced by the presence of a strong external magnetic field. Adopting the cold-plasma polarization tensor to account for the electron component, we find that the polarization properties and transport of x-ray radiation can be severely altered by the magnetic vacuum effects. The effect becomes important at relatively high frequencies, ωωp (15πα)12 BcB where ωp=(4πne e2m)12 is the plasma frequency of the electron component, α is the fine-structure constant, and Bc=m2c3e 4.4×1013 G is the electrodynamic critical field. For typical pulsar magnetic fields, B∼0.1 Bc, and x-ray frequencies, this condition is satisfied even for relatively high plasma densities ne∼1023 cm-3. Whenever the above inequality is fulfilled the vacuum effect dominates the polarization properties of the normal modes of the medium, giving rise to a significant change in the medium opacity. The Thomson, bremsstrahlung, and cyclotron opacities are thus significantly altered from their usual cold-plasma values. The largest departures are found in the vicinity of the electron gyrofrequency, where the vacuum induces a strongly anisotropic resonant behavior on the ordinary mode (which is nonresonant in the usual cold-plasma circumstances). This property may be significant in analyzing the polarization and spectral character of the cyclotron feature in Hercules X-1 and other accreting x-ray pulsars. © 1979 The American Physical Society.