Optical polarization models of quasi-stellar objects and BL Lac objects.

Abstract

view Abstract Citations (47) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Optical polarization models of quasi-stellar objects and BL Lacertae objects. Nordsieck, K. H. Abstract 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. Subject headings: BL Lacertae objects - polarization - quasars synchrotron radiation Publication: The Astrophysical Journal Pub Date: November 1976 DOI: 10.1086/154764 Bibcode: 1976ApJ...209..653N full text sources ADS | data products SIMBAD (2) NED (2)