2017
DOI: 10.1093/mnras/stx256
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18–22 cm VLBA Faraday rotation studies of six AGN jets

Abstract: The formation of relativistic jets in active galactic nuclei (AGN) is related to accretion on to their central supermassive black holes, and magnetic fields are believed to play a central role in launching, collimating and accelerating the jet streams from very compact regions out to kiloparsec or megaparsec scales. In the presence of helical or toroidal magnetic fields threading the AGN jets and their immediate vicinity, gradients in the observed Faraday rotation measures are expected due to the systematic ch… Show more

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Cited by 10 publications
(17 citation statements)
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References 46 publications
(50 reference statements)
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“…• "flip" in the polarization angle in the transition from the optically thin to the optically thick regime does not occur until an optical depth of τ ≃ 6, which is far upstream of the observed VLBI core region, there is no reason to expect severe departures from a linear λ 2 law for the Faraday rotation in the vast majority of cases, and we, like a number of earlier studies (Gabuzda et al 2014(Gabuzda et al , 2015bMotter & Gabuzda 2017), therefore analyzed core-region RM gradients in the same way as those located in the jet, having verified an absence of appreciable deviations from a λ 2 law. Estimation of significance.…”
Section: Observations and Data Reductionsupporting
confidence: 63%
See 1 more Smart Citation
“…• "flip" in the polarization angle in the transition from the optically thin to the optically thick regime does not occur until an optical depth of τ ≃ 6, which is far upstream of the observed VLBI core region, there is no reason to expect severe departures from a linear λ 2 law for the Faraday rotation in the vast majority of cases, and we, like a number of earlier studies (Gabuzda et al 2014(Gabuzda et al , 2015bMotter & Gabuzda 2017), therefore analyzed core-region RM gradients in the same way as those located in the jet, having verified an absence of appreciable deviations from a λ 2 law. Estimation of significance.…”
Section: Observations and Data Reductionsupporting
confidence: 63%
“…Hovatta et al (2012) did not consider potential transverse RM gradients in the vicinity of the VLBI core, on the grounds that this region was at least partially optically thick, increasing the possibility of spurious gradients. This issue has been discussed in a number of recent studies (Motter & Gabuzda 2017, Wardle 2018. Because the expected 90…”
Section: Observations and Data Reductionmentioning
confidence: 98%
“…Polarization maps for all of these sources at 15 GHz can be found in Lister & Homan (2005) and on the MOJAVE website (http://www.physics.purdue.edu/MOJAVE/). Like Motter and Gabuzda (2017), in all cases, we present total intensity (Stokes I) and RM maps made using the naturally weighted elliptical convolving beams as well as circular convolving beams having equal area; in other words, the circular beam used has a full width at half maximum equal to (BM AJ)(BM IN ), where BM AJ and BM IN are the full widths at half maximum for the major and minor axes of the nominal elliptical restoring beam. As is explained by Motter and Gabuzda (2017), the maps made using circular convolving beams were used to test the robustness of RM structures visible in the maps made using the elliptical beams -for example, an RM gradient that seemed to be present in the original RM map but disappeared upon convolution with the equal-area circular beam would not be considered reliable (see, e.g., the case of 2155-152 presented by Gabuzda et al 2015).…”
Section: Resultsmentioning
confidence: 99%
“…Statistically significant transverse RM gradients have now also been reliably detected on scales of several tens to thousands of parsecs in 14 AGN, with tentative transverse RM gradients (whose statistical significances do not reach 3σ or have not yet been determined) observed on such scales in another six AGN [21][22][23]. The collected data for transverse RM gradients observed on parsec to kiloparsec scales clearly indicates a predominance of inward currents near the jet axis on parsec scales and outward currents flowing along the jet farther from the axis on scales greater than a few tens of parsec.…”
Section: Discussionmentioning
confidence: 98%