Helical magnetic fields associated with the relativistic jets of four BL Lac objects

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Gabuzda, Denise
Murray, Éamonn D.
Cronin, Patrick
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Oxford University Press
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Evidence has been 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. 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 across the jets, due to the systematic change in the line-of-sight component of the jet B field. We present evidence for transverse rotation measure 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.
Magnetic fields , Polarization , Radio continuum , Galaxies
Gabuzda, D. C., Murray, É. and Cronin, P. (2004) 'Helical magnetic fields associated with the relativistic jets of four BL Lac objects', Monthly Notices of the Royal Astronomical Society, 351(4), pp. L89-L93. doi: 10.1111/j.1365-2966.2004.08037.x
© 2004, Royal Astronomical Society