Optical circular polarization in two BL Lacertae objects?
Abstract
The authors present results of simultaneous UBVRI linear and circular polarization measurements of the BL Lac objects 0422+004 and 0735+178 and of the quasar 3C 273. For 0422+004 and 0735+178 they obtain a 2σ result 0.2% for the degree of circular polarization. Optical circular polarization at such a level would indicate either stronger magnetic fields than usually assumed, or mechanisms enhancing circular polarization, such as anisotropic electron pitch angle distributions or special global magnetic field geometries. The derived upper limits for magnetic field strengths (from 3σ upper limits for the amount of circularly polarized radiation) are between 1 and 40 kG.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- June 1993
- Bibcode:
- 1993A&A...273..393V
- Keywords:
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- galaxies: active;
- BL Lacertae objects;
- quasars: general