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Session 11 - QSOs and Radio Galaxies.
Display session, Monday, June 08
HST observations of some QSOs show a strong, abrupt increase in polarization at rest wavelength about 750 A (Impey et al. 1995, Ap.J. 440, 80; Koratkar et al. 1995, Ap.J. 450, 501). The feature can be explained in terms of polarized Lyman continuum emission that sets in at wavelength 912 A in the rest frame of gas orbiting in an accretion disk around a supermassive black hole. The observed wavelength of the polarization rise is blueshifted by a combination of relativistic effects. In contrast, any discontinuity at the Lyman edge in the total flux emitted by the disk atmosphere should show a gradual observed onset starting at a wavelength longward of 912 A. Depending on the angular momentum of the black hole and the inclination of the disk to the line of sight, the wavelength of the observed rise should fall between about 640 and 830 A (Shields et al., Ap.J. 496, 743). These expectations are consistent with the observed properties of "Lyman edge candidate" QSOs, including the three objects with observed Lyman continuum polarization rises. We present model results for the observed polarized spectrum and discuss possible physical origins for the polarized Lyman continuum.
This material is based in part upon work supported by the Texas Advanced Research Program under Grant No. 003658-015.
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