First results from 18-22cm VLBA polarisation observations of the MOJAVE-I AGNs

Coughlan, Colm P.; Murphy, Ronan; Enery, Kyle Mc; Patrick, Heather J.; Hallahan, Redmond; Gabuzda, D. C.

doi:10.22323/1.125.0046

Cited by 5 publications

(13 citation statements)

References 2 publications

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“…This RM map was originally published by Coughlan et al (2010); again, we were not able to use the previously published RM map directly because the associated error maps did not take into account the improved method of Hovatta et al (2012) for estimating the on-source Q and U uncertainties in individual pixels.…”

Section: Vlba Datamentioning

confidence: 99%

“…We addressed this by using the Q and U maps used by Coughlan et al (2010) to produce new RM maps in both AIPS and CASA, assigning Q and U uncertainties in accordance with the approach of Hovatta et al (2012).…”

Section: Vlba Datamentioning

confidence: 99%

“…Of these, two (5C4.114 and A2142A) have now been shown to be statistically significant (Gabuzda et al 2015b; this paper), leaving six additional tentative gradients. To these we add results for 3C 120 on slightly smaller scales of 30-100 pc presented by Coughlan et al (2010). We have not attempted to measure or analyse the magnitudes of these tentative RM gradients, which would be extremely difficult to interpret unambiguously due to convolution with the observing beam.…”

Section: Tentative Gradients From An Initial Inspection Of Rm Maps Inmentioning

confidence: 99%

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Dominance of outflowing electric currents on decaparsec to kiloparsec scales in extragalactic jets

Christodoulou

Gabuzda

Knuettel

et al. 2016

A&A

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Context. Helical magnetic fields embedded in the jets of active galactic nuclei (AGNs) are required by the broad range of theoretical models that advocate for electromagnetic launching of the jets. In most models, the direction of the magnetic field is random, but if the axial field is generated by a Cosmic Battery generated by current in the direction of rotation in the accretion disk, there is a correlation between the directions of the spin of the AGN accretion disk and of the axial field, which leads to a specific direction for the axial electric current, azimuthal magnetic field, and the resulting observed transverse Faraday-rotation (FR) gradient across the jet, due to the systematic change in the line-of-sight magnetic field. Aims. We consider new observational evidence for the presence of a nested helical magnetic-field structure such as would be brought about by the operation of the Cosmic Battery, and make predictions about the expected behavior of transverse FR gradients observed on decaparsec and kiloparsec scales. Methods. We have jointly considered 27 detections of transverse FR gradients on parsec scales, four reports of reversals in the directions of observed transverse FR gradients observed on parsec-decaparsec scales, and five detections of transverse FR gradients on decaparsec-kiloparsec scales, one reported here for the first time. We also consider seven tentative additional examples of transverse FR gradients on kiloparsec scales, based on an initial visual inspection of published Very Large Array FR maps of 85 extragalactic radio sources, for three of which we have carried out quantitative analyses in order to quantitatively estimate the significances of the gradients. Results. The data considered indicate a predominance of transverse FR gradients in the clockwise direction on the sky (i.e., net axial current flowing inward in the jet) on parsec scales and in the counter-clockwise direction on the sky (i.e., net axial current flowing outward) on scales greater than about 10 pc, consistent with the expectations for the Cosmic Battery. The predominance of counter-clockwise FR gradients on larger scales has been established at the 3σ confidence level. Conclusions. The collected results provide evidence for a reversal in the direction of the net azimuthal magnetic field determining the ordered component of the observed FR images, with distance from the jet base. This can be understood if the dominant azimuthal field on parsec scales corresponds to an axial electric current flowing inward along the jet, whereas the (weaker) dominant azimuthal field on kiloparsec scales corresponds to a outward-flowing current in the outer sheath of the jet and/or an extended disk wind. This is precisely the current/magnetic field structure that should be generated by the Cosmic Battery.

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Section: Vlba Datamentioning

confidence: 99%

Section: Vlba Datamentioning

confidence: 99%

Section: Tentative Gradients From An Initial Inspection Of Rm Maps Inmentioning

confidence: 99%

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Dominance of outflowing electric currents on decaparsec to kiloparsec scales in extragalactic jets

Christodoulou

Gabuzda

Knuettel

et al. 2016

A&A

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“…The observations analysed in this work were made simultaneously at 1358, 1430, 1493, and 1665 MHz (22.1, 21.0, 20.1, and 18.0 cm) with the National Radio Astronomy Observatory (NRAO) VLBA at various epochs in 2010 at a total aggregate bit rate of 128 Mbits/s, observing each source in snapshot mode [14]. The amplitude, phase, polarization, and electric vector position angle (EVPA) calibrations were done in the NRAO Astronomical Imaging Processing System (AIPS) using standard techniques, using Los Alamos as the reference antenna.…”

Section: Observations and Data Analysismentioning

confidence: 99%

18–22 cm VLBA Observational Evidence for Toroidal B-Field Components in Six AGN Jets

Motter

Gabuzda

2016

Galaxies

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Abstract:The formation of relativistic jets in Active Galactic Nuclei (AGN) is related to accretion onto their central supermassive black holes, and magnetic (B) fields are believed to play a central role in launching, collimating, and accelerating the jet streams from very compact regions out to kiloparsec scales. We present results of Faraday rotation studies based on Very Long Baseline Array (VLBA) data obtained at 18-22 cm for six well known AGN (OJ 287, 3C 279, PKS 1510-089, 3C 345, BL Lac, and 3C 454.3), which probe projected distances out to tens of parsecs from the observed cores. We have identified statistically significant, monotonic, transverse Faraday rotation gradients across the jets of all but one of these sources, indicating the presence of toroidal B fields, which may be one component of helical B fields associated with these AGN jets.

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“…The RM maps were made in AIPS and CASA. Some further information about the observations and their calibration can be found in [11].…”

Section: Observationsmentioning

confidence: 99%

18-22 cm VLBA observations of three BL Lac objects

Healy¹,

Gabuzda²

2016

Proceedings of 11th European VLBI Network Symposium &Amp; Users Meeting — PoS(11th EVN Symposium)

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VLBA polarization observations of the 135 AGNs in the MOJAVE-I sample have recently been obtained at four frequencies between 1.3 and 1.7 GHz. These observations are sensitive to compact radio emission on scales from a few to tens of parsecs from the VLBA core. VLBA observations at the same frequencies were obtained earlier for 34 BL Lac objects, enabling a multiepoch study of the extended radio jets of these objects. As an initial step in this study, we have constructed new images for three BL Lac objects with rich jet structures: 0735+178, 1803+784 and 2200+420 (BL Lac), which are analyzed together with the previous results of Hallahan and Gabuzda (2008). We consider the morphology, polarization (magnetic field) structure and Faraday rotation distributions of these objects.11th European VLBI Network Symposium Users Meeting,

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First results from 18-22cm VLBA polarisation observations of the MOJAVE-I AGNs

Cited by 5 publications

References 2 publications

Dominance of outflowing electric currents on decaparsec to kiloparsec scales in extragalactic jets

Dominance of outflowing electric currents on decaparsec to kiloparsec scales in extragalactic jets

18–22 cm VLBA Observational Evidence for Toroidal B-Field Components in Six AGN Jets

18-22 cm VLBA observations of three BL Lac objects

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