The 15-43 GHz parsec-scale circular polarization of 41 active galactic nuclei

Show simple item record Vitrishchak, V. M. Gabuzda, Denise Algaba, Juan Carlos Rastorgueva, E. A. O'Sullivan, Shane P. O'Dowd, A. 2017-11-07T09:38:56Z 2017-11-07T09:38:56Z 2008
dc.identifier.citation Vitrishchak, V. M., Gabuzda, D. C., Algaba, J. C., Rastorgueva, E. A., O'Sullivan, S. P. and O'Dowd, A. (2008) 'The 15–43 GHz parsec-scale circular polarization of 41 active galactic nuclei', Monthly Notices of the Royal Astronomical Society, 391(1), pp. 124-135. doi: 10.1111/j.1365-2966.2008.13919.x en
dc.identifier.volume 391
dc.identifier.issued 1
dc.identifier.startpage 124
dc.identifier.endpage 135
dc.identifier.issn 0035-8711
dc.identifier.doi 10.1111/j.1365-2966.2008.13919.x
dc.description.abstract We present the results of parsec-scale circular-polarization measurements based on Very Long Baseline Array data for a number of radio-bright, core-dominated active galactic nuclei obtained simultaneously at 15, 22 and 43 GHz. The degrees of circular polarization m(c) for the Very Long Baseline Interferometry (VLBI) core region at 15 GHz are similar to the values reported earlier at this wavelength, with typical values of a few tenths of a per cent. We find that mc as often rises as falls with increasing frequency between 15 and 22 GHz, while the degree of circular polarization at 43 GHz is in all cases higher than at 22 and 15 GHz. This behaviour seems contrary to expectations, since the degree of circular polarization from both synchrotron radiation and the Faraday conversion of linear to circular polarization - the two main mechanisms considered thus far in the literature - should decrease towards higher frequencies if the source is homogeneous. The increase in mc at 43 GHz may be due to the presence of regions of both positive and negative circular polarization with different frequency dependences ( but decreasing with increasing frequency) on small scales within the core region; alternatively, it may be associated with the intrinsic inhomogeneity of a Blandford-Konigl like jet. In several objects, the detected circular polarization appears to be near, but not coincident with, the core, although further observations are needed to confirm this. We find several cases of changes in sign with frequency, most often between 22 and 43 GHz. We find tentative evidence for transverse structure in the circular polarization of 1055+018 and 1334-127, that is consistent with their being generated by either the synchrotron mechanism or the Faraday conversion in a helical magnetic field. Our results confirm the earlier finding that the sign of the circular polarization at a given observing frequency is generally consistent across epochs separated by several years or more, suggesting stability of the magnetic-field orientation in the innermost jets. en
dc.format.mimetype application/pdf en
dc.language.iso en en
dc.publisher Oxford University Press en
dc.rights © 2008, the Authors. Journal compilation © 2008, RAS en
dc.subject Active en
dc.subject Galaxies en
dc.subject Jets en
dc.subject Quasars en
dc.subject General en
dc.title The 15-43 GHz parsec-scale circular polarization of 41 active galactic nuclei en
dc.type Article (peer-reviewed) en
dc.internal.authorcontactother Denise Gabuzda, 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.description.status Peer reviewed en
dc.identifier.journaltitle Monthly Notices of the Royal Astronomical Society en
dc.internal.IRISemailaddress en

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