The Formation and Disruption of Black Hole Jets by Ioannis Contopoulos Denise Gabuzda & Nikolaos Kylafis

Author:Ioannis Contopoulos, Denise Gabuzda & Nikolaos Kylafis
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

5.5.2 Magnetic-Field Structures

The observed degrees of polarization in the jets of AGN range from a few percent up to 50–60 %, fully consistent with the jet emission being incoherent synchrotron radiation in a partially ordered B field. In most cases, the observed polarization vectors – and therefore the associated jet B fields – in the VLBI jets of AGN tend to be either parallel or perpendicular to the local jet direction. This should come about naturally if the jets locally exhibit approximately cylindrical symmetry: the B field can always be separated into longitudinal and transverse components projected onto the sky (e.g. Lyutikov et al. 2005).

Various polarization patterns are fairly commonly, illustrated schematically in Fig. 5.4, which shows an intensity image taken from the website of the MOJAVE project (see the Acknowledgements) with artificial polarization sticks superimposed (recall that the observed polarization is orthogonal to the underlying B field in optically thin regions, such as the jet). Possible origins for each of these patterns are considered below.

Fig. 5.4Schematics of various polarization patterns commonly observed in AGN jets, corresponding to: (a) extended regions of longitudinal field; (b) regions of orthogonal field associated with bright, compact regions; (c) extended regions of orthogonal field; (d) spine–sheath transverse B-field structure; (e) longitudinal field offset toward one side of the jet; (f) longitudinal field around a bend in the jet. Recall that the B field is orthogonal to the observed polarization in optically thin regions. The contour map was taken from the MOJAVE website (see the Acknowledgements), and the sticks added to illustrate the various polarization configurations

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