Astrophysical Masers. 11. Polarization Properties

The equations governing the transfer of polarized radiation in astrophysical masers are derived. It is found that the magnetic field and the plasma in maser sources play a central role in determining the polarization of the emitted radiation. The character of the polarization depends upon the relative sizes of the decay constant of the maser levels, F; the stimulated-emission rate R; the Zeeman splitting, g and the bandwidth of the amplified radiation, Aw. Unsaturated masers (R < F) emit unpolarized radiation unless g > Aw. For g > A they amplify the Zeeman pattern if the Faraday rotation per gain length in the source is small. If the Faraday rotation per gain length is large, then the a components of the Zeeman pattern are 100 percent circularly polarized and the n component is unpolarized. Saturated masers (R > F) emit unpolarized radiation unless g > (RF)"2. If the Faraday rotation across the region of saturated amplification is small, the emitted radiation is partially linearly polarized for (RF)"2 < g Aw whereas for g > Aw it is just the amplified Zeeman pattern. If the Faraday rotation across the saturated region is large, all linear polarization is destroyed. For g > Aw, the a components of the Zeeman pattern are again 100 percent circularly polarized. Subject headings: masers - polarization - radiative transfer - Zeeman effect