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

dc.contributor.authorMahmud, Mehreen
dc.contributor.authorGabuzda, Denise
dc.contributor.authorBezrukovs, V.
dc.contributor.funderScience Foundation Ireland
dc.date.accessioned2017-11-07T09:38:55Z
dc.date.available2017-11-07T09:38:55Z
dc.date.issued2009
dc.description.abstractSeveral 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.sponsorshipScience Foundation Ireland (Basic Research Grant)en
dc.description.statusPeer revieweden
dc.description.versionPublished Versionen
dc.format.mimetypeapplication/pdfen
dc.identifier.citationMahmud, 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.xen
dc.identifier.doi10.1111/j.1365-2966.2009.15013.x
dc.identifier.endpage12
dc.identifier.issn0035-8711
dc.identifier.issued1
dc.identifier.journaltitleMonthly Notices of the Royal Astronomical Societyen
dc.identifier.startpage2
dc.identifier.urihttps://hdl.handle.net/10468/4968
dc.identifier.volume400
dc.language.isoenen
dc.publisherOxford University Pressen
dc.relation.urihttps://academic.oup.com/mnras/article-lookup/doi/10.1111/j.1365-2966.2009.15013.x
dc.rights© 2009, the Authors. Journal compilation © 2009, RASen
dc.subjectBL Lacertae objectsen
dc.subjectIndividualen
dc.subjectB1803+784en
dc.subjectJetsen
dc.subjectGalaxiesen
dc.subjectMagnetic fieldsen
dc.titleSurprising evolution of the parsec-scale Faraday Rotation gradients in the jet of the BL Lac object B1803+784en
dc.typeArticle (peer-reviewed)en
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