Optical polarization models of quasi-stellar objects and BL Lacertae objects

Journal Article · Mon Nov 01 04:00:00 EST 1976 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/154764· OSTI ID:7330110

Nordsieck, K H

A model for optically thin synchrotron radiation from a region of partially aligned magnetic field is compared with optical linear polarization data for QSOs and BL Lacertae objects. The synchrotron theory is treated by considering the magnitude and angle of the field perpendicular to the line of sight to be described by a probability distribution. A quite general argument shows that on such a model the linear polarization should depend much more steeply on the spectral index of the radiation than it does in the case of a perfectly aligned field. For two general classes of field asymmetry, the polarization usually depends linearly or quadratically on the spectral index and on the square of the field alignment, for small values of the alignment. QSO data from the literature together with new observations of BL Lacertae objects are gathered together and compared with this model; a 15--20 percent upper limit for the field alignment is consistent with the polarization of the nonvariable objects and the quiescent polarization of the variables, while the highly polarized bursts of the variables require less than a factor of 2 enhancement in the alignment. For objects with curved spectra, perhaps due to upper energy cutoffs in the electron spectrum, the theory predicts a polarization which rises gradually with frequency. This polarization wavelength dependence is weak over the optical band, but should be easily observable in those BL Lacertae objects with curved spectra, once polarization observations have been extended beyond the optical window. A possible observation of this effect in PKS 0735+17 in the optical on three nights is presented. (AIP)

• Research Organization: Washburn Observatory, University of Wisconsin, Madison
• OSTI ID: 7330110
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 209:3; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640103* -- Astrophysics & Cosmology-- Quasi-Stellar
Radio
& X-Ray Sources-- (-1987)
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
BREMSSTRAHLUNG
COSMIC RADIO SOURCES
ELECTROMAGNETIC RADIATION
ELECTRON SPECTRA
MAGNETIC FIELD CONFIGURATIONS
MAGNETIC FIELDS
MATHEMATICAL MODELS
POLARIZATION
QUASARS
RADIATIONS
SPECTRA
STAR MODELS
SYNCHROTRON RADIATION