Surprising evolution of the parsec-scale Faraday Rotation gradients in the jet of the BL Lac object B1803+784

Show simple item record Mahmud, Mehreen Gabuzda, Denise Bezrukovs, V. 2017-11-07T09:38:55Z 2017-11-07T09:38:55Z 2009
dc.identifier.citation Mahmud, M., Gabuzda, D. C. and Bezrukovs, V. (2009) 'Surprising evolution of the parsec-scale Faraday Rotation gradients in the jet of the BL Lac object B1803+784', Monthly Notices of the Royal Astronomical Society, 400(1), pp. 2-12. doi: 10.1111/j.1365-2966.2009.15013.x en
dc.identifier.volume 400
dc.identifier.issued 1
dc.identifier.startpage 2
dc.identifier.endpage 12
dc.identifier.issn 0035-8711
dc.identifier.doi 10.1111/j.1365-2966.2009.15013.x
dc.description.abstract Several multifrequency polarization studies have shown the presence of systematic Faraday Rotation gradients across the parsec-scale jets of active galactic nuclei, taken to be due to the systematic variation of the line-of-sight component of a helical magnetic (B) field across the jet. Other studies have confirmed the presence and sense of these gradients in several sources, thus providing evidence that these gradients persist over time and over large distances from the core. However, we find surprising new evidence for a reversal in the direction of the Faraday Rotation gradient across the jet of B1803+784, for which multifrequency polarization observations are available at four epochs. At our three epochs and the epoch of Zavala & Taylor, we observe transverse rotation measure (RM) gradients across the jet, consistent with the presence of a helical magnetic field wrapped around the jet. However, we also observe a 'flip' in the direction of the gradient between 2000 June and 2002 August. Although the origins of this phenomenon are not entirely clear, possibly explanations include (i) the sense of rotation of the central supermassive black hole and accretion disc has remained the same, but the dominant magnetic pole facing the Earth has changed from north to south, (ii) a change in the direction of the azimuthal B field component as a result of torsional oscillations of the jet and (iii) a change in the relative contributions to the observed RMs of the 'inner' and 'outer' helical fields in a magnetic-tower model. Although we cannot entirely rule out the possibility that the observed changes in the RM distribution are associated instead with changes in the thermal-electron distribution in the vicinity of the jet, we argue that this explanation is unlikely. en
dc.description.sponsorship Science Foundation Ireland (Basic Research Grant) en
dc.format.mimetype application/pdf en
dc.language.iso en en
dc.publisher Oxford University Press en
dc.rights © 2009, the Authors. Journal compilation © 2009, RAS en
dc.subject BL Lacertae objects en
dc.subject Individual en
dc.subject B1803+784 en
dc.subject Jets en
dc.subject Galaxies en
dc.subject Magnetic fields en
dc.title Surprising evolution of the parsec-scale Faraday Rotation gradients in the jet of the BL Lac object B1803+784 en
dc.type Article (peer-reviewed) en
dc.internal.authorcontactother Mehreen Mahmud, Physics, University College Cork, Cork, Ireland. +353-21-490-3000 Email: en
dc.internal.availability Full text available en
dc.description.version Published Version en
dc.contributor.funder Science Foundation Ireland
dc.description.status Peer reviewed en
dc.identifier.journaltitle Monthly Notices of the Royal Astronomical Society en
dc.internal.IRISemailaddress en

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