High Levels of Circular Polarization

We present multi-frequency, high resolution VLBA circular polarization images of the radio source 3C 84 in the center of NGC 1275. Our images reveal a complex distribution of circular polarization in the inner parsec of the radio jet, with local levels exceeding 3% polarization, the highest yet detected with VLBI techniques. The circular polarization changes sign along the jet, making 3C 84 also the first radio jet to show both signs of circular polarization simultaneously. The spectrum and changing sign of the circular polarization indicate that it is unlikely to be purely intrinsic to the emitted synchrotron radiation. The Faraday conversion process makes a significant and perhaps dominant contribution to the circular polarization, and the observed spectrum suggests the conversion process is near saturation. The sign change in the circular polarization along the jet may result from this saturation or may be due to a change in magnetic field order after an apparent bend in the jet. From the small spatial scales probed here, ≃ 0.15 pc, and the comparably high levels of circular polarization inferred for the intra-day variable source PKS 1519−273, we suggest a connection between small spatial scales and efficient production of circular polarization. Subject headings: galaxies : active — galaxies: jets — galaxies: individual: 3C 84, NGC 1275 — polarization