On the Origin of Polarization near the Lyman Edge in Quasars

Abstract

Optical/UV radiation from accretion disks in quasars is likely to be partly scattered by a hot plasma enveloping the disk. We investigate whether the scattering may produce the steep rises in polarization observed blueward of the Lyman limit in some quasars. We suggest and assess two models. In the first model, primary disk radiation with a Lyman edge in absorption passes through a static ionized "skin" covering the disk, which has a temperature about 3 keV and a Thomson optical depth about unity. Electron scattering in the skin smears out the edge and produces a steep rise in polarization at lambda < 912 A. In the second model, the scattering occurs in a hot coronal plasma outflowing from the disk with a mildly relativistic velocity. We find that the second model better explains the data. The ability of the models to fit the observed rises in polarization is illustrated with the quasar PG 1630+377.

submitted to ApJ Letters

References in corpus (6)

• Plasma Ejection from Magnetic Flares and the X-ray Spectrum of Cygnus X-1
• Correlation between Compton reflection and X-ray slope in Seyferts and X-ray binaries
• Electron-Positron Outflows from Gamma-Ray Emitting Accretion Discs
• Polarization change due to fast winds from accretion disks
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Cited by in corpus (9)

• A Structure for Quasars
• X-ray spectra of accretion discs with dynamic coronae
• Polarized X-rays from windy accretion in Cygnus X-1
• High-precision optical polarimetry of the accreting black hole V404 Cyg during the June 2015 outburst
• Evolving optical polarisation of the black hole X-ray binary MAXI J1820+070
• Accretion Disk Models of Luminous Black Holes
• Variability of X-ray polarization of Cyg X-1
• A Structure for Quasars
• The Lyman Continuum Polarization Rise in the QSO PG 1222+228