75 research outputs found
Helical Magnetic Fields Associated with the Relativistic Jets of Four BL Lac Objects
Evidence has been mounting that many of the transverse jet B fields observed
in BL Lac objects on parsec scales represent the dominant vvroidal compoent of
the intrinsic jet B fields. Such fields could come about, for example, as a
result of the "winding up" of an initial "seed" field with a significant
longitudinal component by the rotation of the central accreting object. If this
is the case, this should give rise to gradients in the rotation measure (RM)
across the jets, due to the systematic change in the line-of-sight component of
the jet B field. We present evidence for transverse RM gradients in four BL Lac
objects, strengthening arguments that the jets of these objects do indeed have
toroidal or helical B fields. This underlines the view of the jets as
fundamentally electromagnetic structures, and suggests that they may well carry
non-zero currents. It also provides a natural means to collimate the jets.Comment: 6 pages, 2 figures, accepted for publication in MNRAS Letter
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