Parsec scale Faraday-rotation structure across the jets of nine active galactic nuclei

We briefly review how opacity affects the observed polarization in synchrotron emitting jets. We show some new multi-frequency observations of 3C 273 made with the VLBA in 1999–2000, which add significantly to the available rotation measure (RM) observations of this source. Our findings can be summarized as follows: (1) The transverse gradient in RM is amply confirmed. This implies a toroidal component to the magnetic field, which in turn requires a current of 1017–1018 A flowing down the jet. (2) The net magnetic field in the jet is longitudinal; however, whether or not the longitudinal component is vector-ordered is an open question. (3) The RM distribution is variable on timescales of months to years. We attribute this to the motion of superluminal components behind a turbulent Faraday screen that surrounds the jet. (4) Finally, we suggest that Faraday rotation measurements at higher resolution and higher frequencies, with the Event Horizon Telescope, may enable useful constraints to be placed on the accretion rate onto the central black hole.

Section: New Vlba Images Of 3c 273 and The Variable Transverse Gradimentioning

confidence: 59%

The Variable Rotation Measure Distribution in 3C 273 on Parsec Scales

Wardle

2018

“…This theoretical picture is supported by indirect observational evidence (AGN warm absorbers [4], Faraday RM gradients across astrophysical jets [5][6][7], polarization measurements [8], XRB Hardness-Intensity q-diagrams [9], GRB exponential afterglow decay [10], etc. ), and by state-of-the-art MHD simulations [11].…”

Section: Introductionmentioning

confidence: 78%

“…In all such cases, the inner/outer currents flow toward/away from the origin respectively. In the context of the Cosmic Battery, we are compelled to associate the observationally inferred reversed inward flowing electric current near the origin with the inner (spine) jet mentioned above [7,20].…”

Section: The Cosmic Batterymentioning

confidence: 99%

Electric Currents along Astrophysical Jets

Contopoulos

2017

Astrophysical black holes and their surrounding accretion disks are believed to be threaded by grand design helical magnetic fields. There is strong theoretical evidence that the main driver of their winds and jets is the Lorentz force generated by these fields and their associated electric currents. Several researchers have reported direct evidence for large scale electric currents along astrophysical jets. Quite unexpectedly, their directions are not random as would have been the case if the magnetic field were generated by a magnetohydrodynamic dynamo. Instead, in all kpc-scale detections, the inferred electric currents are found to flow away from the galactic nucleus. This unexpected break of symmetry suggests that a battery mechanism is operating around the central black hole. In the present article, we summarize observational evidence for the existence of large scale electric currents and their associated grand design helical magnetic fields in kpc-scale astrophysical jets. We also present recent results of general relativistic radiation magnetohydrodynamic simulations which show the action of the Cosmic Battery in the vicinity of astrophysical black holes.

“…The first observational signature of such a transverse RM gradient was reported in the pc-scale jet of 3C 273 [174]. To date, transverse RM gradients have been reported in ∼30 pc-scale jets (see, e.g., in [165,[175][176][177][178][179][180][181][182]). Moreover, as mentioned before, the recent high resolution polarimetric studies with GMVA and RadioAstron have revealed transverse RM gradients even closer to the jet base [146,150], implying that helical B-fields in jets are preserved over a wide range of distances from the innermost regions to far beyond the VLBI core.…”

Section: Polarimetric Propertiesmentioning

confidence: 97%

Relativistic Jets from AGN Viewed at Highest Angular Resolution

Hada

2019

Accreting supermassive black holes in active galactic nuclei (AGN) produce powerful relativistic jets that shine from radio to GeV/TeV γ-rays. Over the past decade, AGN jets have extensively been studied in various energy bands and our knowledge about the broadband emission and rapid flares are now significantly updated. Meanwhile, the progress of magnetohydrodynamic simulations with a rotating black hole have greatly improved our theoretical understanding of powerful jet production. Nevertheless, it is still challenging to observationally resolve such flaring sites or jet formation regions since the relevant spatial scales are tiny. Observations with very long baseline interferometry (VLBI) are currently the only way to directly access such compact scales. Here we overview some recent progress of VLBI studies of AGN jets. As represented by the successful black hole shadow imaging with the Event Horizon Telescope, the recent rapid expansion of VLBI capability is remarkable. The last decade has also seen a variety of advances thanks to the advent of RadioAstron, GMVA, new VLBI facilities in East Asia as well as to the continued upgrade of VLBA. These instruments have resolved the innermost regions of relativistic jets for a number of objects covering a variety of jetted AGN classes (radio galaxies, blazars, and narrow-line Seyfert 1 galaxies), and the accumulated results start to establish some concrete (and likely universal) picture on the collimation, acceleration, recollimation shocks, magnetic field topology, and the connection to high-energy flares in the innermost part of AGN jets.