In Search of Evidence for Toroidal B Fields Associated with the Jets of AGN

Abstract

Evidence is mounting that many of the transverse jet B fields observed in BL Lac objects on parsec scales represent the dominant toroidal component of the intrinsic jet B fields. If this is the case, this may give rise to rotation-measure (RM) gradients across the jets, due to the systematic change in the line-of-sight component of the jet B field. We have found evidence for such RM gradients in several BL Lac objects. We discuss these new results, together with some of their implications for our understanding of the pc-scale jets of AGN.