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Paper: Rotation Measure Observation towards NRAO 140 Jet: Constraints for the Pitch Angle of a Helical Magnetic Field
Volume: 386, Extragalactic Jets: Theory and Observation from Radio to Gamma Ray
Page: 513
Authors: Asada, K.; Inoue, M.; Nakamura, M.; Kameno, S.; Nagai, H.
Abstract: We show a systematic gradient in the distribution of Faraday Rotation Measure (RM), and the sign of its RM is different at both sides of jet respect to the jet axis. Sign of RM changes only by direction of the magnetic field along the line of sight, so that it can be naturally explained by an existence of helical magnetic components associated with the jet itself as supported by the magnetohydrodynamic jet models. Taking into account the viewing angle of the jet, we derived two constraints for the pitch angle of the helical magnetic field from the distribution of Rotation Measure and the projected magnetic field. The distribution of RM implies the helical magnetic fields are tightly wound, while that of the projected magnetic field support they are loosely wound, around the jet axis. This difference can arise if the Faraday Rotator is not co-exist with the emitting region. Our results may accept a physical picture that the ultra-relativistic jet (spine) with loosely wound helical magnetic field is surrounded by sub-relativistic wind layer (sheath) with the tightly wound helical magnetic field.
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