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Vacuum polarization effects on radiative opacities in a strong magnetic field

1979; American Physical Society; Volume: 19; Issue: 12 Linguagem: Inglês

10.1103/physrevd.19.3565

1538-4500

P. Mészáros, J. Ventura,

Magnetic confinement fusion research

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, $\frac{\ensuremath{\omega}}{{\ensuremath{\omega}}_{p}}\ensuremath{\gtrsim}{(\frac{15\ensuremath{\pi}}{\ensuremath{\alpha}})}^{\frac{1}{2}}$ $\frac{{B}_{c}}{B}$ where ${\ensuremath{\omega}}_{p}={(4\ensuremath{\pi}{n}_{e}\frac{{e}^{2}}{m})}^{\frac{1}{2}}$ is the plasma frequency of the electron component, $\ensuremath{\alpha}$ is the fine-structure constant, and ${B}_{c}=\frac{{m}^{2}{c}^{3}}{e\ensuremath{\hbar}}\ensuremath{\simeq}4.4\ifmmode\times\else\texttimes\fi{}{10}^{13}$ G is the electrodynamic critical field. For typical pulsar magnetic fields, $B\ensuremath{\sim}0.1$ ${B}_{c}$, and x-ray frequencies, this condition is satisfied even for relatively high plasma densities ${n}_{e}\ensuremath{\sim}{10}^{23}$ ${\mathrm{cm}}^{\ensuremath{-}3}$. 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.