The Lyman Continuum Polarization Rise in the QSO PG 1222+228

Some QSOs show an abrupt, strong rise in polarization near rest wavelength750 A. If this arises in the atmosphere of an accretion disk around asupermassive black hole, it may have diagnostic value. In PG 1222+228, thepolarization rise occurs at the wavelength of a sharp drop in flux. We examineand reject interpretations of this feature involving a high velocity outflow.The observations agree with a model involving several intervening Lyman limitsystems, two of which happen to coincide with the Lyman continuum polarizationrise. After correction for the Lyman limit absorption, the continuum shortwardof 912 A is consistent with a typical power-law slope, alpha = -1.8. Thisviolates the apparent pattern for the Lyman limit polarization rises to occuronly in ``candidate Lyman edge QSOs''. The corrected, polarized flux risesstrongly at the wavelength of the polarization rise, resembling the case of PG1630+377. The rise in polarized flux places especially stringent requirementson models.Comment: 19 pages, including 5 EPS figures. Uses aaspp4.sty. Accepted for publication in Publications of the Astronomical Society of the Pacific, 2000 Ma