Polarized cyclotron emission from three-dimensional accretion shocks

The polarized radiation from accretion shocks with a three-dimensional structure are calculated for the first time. It is shown that, because of inhomogeneities along the flow lines, accretion columns with a uniform accretion rate across the column can also produce flat optical/IR spectra as has been noted previously for uniform temperature models with nonuniform accretion across the column. For an accretion column with an axisymmetrically varying accretion rate across, the emission region consists roughly of a high-Lambda region near the symmetry axis at the base of the accretion column and a low-Lambda region near the rim of the shock surface. Such an inhomogeneous emission region emits stronger circular polarization in the red/IR bands and weaker polarization in the blue/UV bands than previous models. If the accretion rate is asymmetric, the polarization light curves become asymmetric, and the linear polarization pulses have different heights and widths. For extremely asymmetric accretion, linear polarization pulses may occur only once per orbital cycle as is often observed, thus providing an alternative explanation for the phenomenon. 32 refs