Accretion Disks and the Lyman Continuum Polarization of QSOs

Abstract

HST observations of some QSOs show a strong, abrupt increase in polarization at rest wavelength about 750 A, suggestive of a connection with the Lyman edge of hydrogen. Blaes and Agol (1996) have proposed an explanation in terms of stellar atmosphere effects in an accretion disk around a supermassive black hole. We have computed the polarized spectrum of a such a disk, including the effects of the relativistic transfer function. Relativistic effects add an additional blueshift of the polarization rise sufficient that the model cannot explain the observations. A good fit results if the emitted radiation is assumed to have a sharp increase in polarized flux at the Lyman edge in the rest frame of the orbiting gas. Relativistic effects then cause the observed polarization to rise sharply at a wavelength substantially less than 912 A. The blueshift depends on the angular momentum of the black hole and the inclination of the disk. A good fit to PG 1630+377 results from a simple model with a dimensionless angular momentum a = 0.5 and an observer viewing angle cos theta = 0.1. An intermediate value of a might result from coallescing black holes, successive accretion events, or electromagnetic extraction of angular momentum from the hole.

24 pages incl. 9 PostScript figures. Uses aaspp4.sty and flshrt.sty. To be published in The Astrophysical Journal, Vol. 496 (1988 April 1)

References in corpus (3)

• On the spin paradigm and the radio dichotomy of quasars
• Non-LTE Models and Theoretical Spectra of Accretion Disks in Active Galactic Nuclei
• Polarization from magnetized accretion discs: II. The effects of absorption opacity on Faraday rotation

Cited by in corpus (7)

• Non-LTE Models and Theoretical Spectra of Accretion Disks in Active Galactic Nuclei. III. Integrated Spectra for Hydrogen-Helium Disks
• Energy distribution of individual quasars from far-UV to X-rays: I. Intrinsic UV hardness and dust opacities
• On the Origin of Polarization near the Lyman Edge in Quasars
• Below the Lyman Edge: UV Polarimetry of Quasars
• Compton scattering of polarized radiation in two phase accretion disks in active galactic nuclei
• The relationship between variable and polarized optical spectral components of luminous type 1 non-blazar quasars
• The Lyman Continuum Polarization Rise in the QSO PG 1222+228