1997/11/18 by G. A. Shields, Gregory A. Shields, Lance Wobus +2 · 11 citations
Physics and Astronomy · #Accretion disc #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Astrophysics and Star Formation Studies #Galaxies: Formation, Evolution, Phenomena #Galaxy #Hubble space telescope #Optics #Physics #Polarization (electrochemistry) #QSOS #Quasar #Stars #Wavelength #astro-ph
paper · pdf · doi:10.1086/305416
published in The Astrophysical Journal 496(2), 743-751 (IOP Publishing) · 24 pages incl. 9 PostScript figures. Uses aaspp4.sty and flshrt.sty. To be published in The Astrophysical Journal, Vol. 496 (1988 April 1)
arxiv created 1997/11/18 · openalex publication_date 1998/04/01 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
Hubble Space T elescope observations of some QSOs show a strong, abrupt increase in polarization at rest wavelength about 750 Å. The closeness of the polarization rise to the H I Lyman edge suggests a connection, but the displacement to shorter wavelengths and the shape of the polarization rise require explanation. We have computed the polarized spectrum of a thermally emitting accretion disk around a supermassive black hole, including the effects of the relativistic transfer function. The local stellar atmosphere spectra show a blueshifted polarization rise in the Lyman continuum, as found by Blaes & Agol in 1996. However, the relativistic transfer function adds an additional blueshift of sufficient magnitude that the model cannot explain the observations. We show that 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 Å. 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 * ≡ cJ / M 2 = 0.5, and an observer viewing angle μ o ≡ cos θ o = 0.1. Smaller values of a * give insufficient blueshifts, and values close to a * = 0.9982 require unrealistically large polarizations in the rest frame of the gas. An intermediate value of a * might result from coalescence of black holes, successive accretion events, or electromagnetic extraction of angular momentum from the hole.