Probing the innermost regions of AGN jets and their magnetic fields with RadioAstron

Bruni, G.; Gómez, J. L.; Casadio, C.; Lobanov, A. P.; Kovalev, Y. Y.; Sokolovsky, K. V.; Lisakov, M. M.; Bach, U.; Marscher, A. P.; Jorstad, Svetlana G.; Anderson, J. M.; Krichbaum, T. P.; Savolainen, Tuomas; Vega-García, L.; Fuentes, Antonio; Zensus, J. A.; Alberdi, A.; Lee, S. S.; Lu, Ru-Sen; Ros, E.

doi:10.1051/0004-6361/201731220

Cited by 34 publications

(25 citation statements)

References 25 publications

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“…With this criterion, C0-1 and C0-2 might be still classified as the VLBI core. However, long-term and high-resolution observations of blazar jets find that compact and bright jet components near the VLBI core often have higher brightness temperatures than the cores determined by the jet kinematics (see, e.g., Lisakov et al 2017;Bruni et al 2017;Jorstad et al 2017). Thus, identifying C0-1 and C0-2 as the potential VLBI core based on the flux density and brightness temperature may not be strongly supported in our observations.…”

Section: Kinematic Referencementioning

confidence: 63%

Event Horizon Telescope imaging of the archetypal blazar 3C 279 at an extreme 20 microarcsecond resolution

Kim

Krichbaum²,

Broderick³

et al. 2020

A&A

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3C 279 is an archetypal blazar with a prominent radio jet that show broadband flux density variability across the entire electromagnetic spectrum. We use an ultra-high angular resolution technique – global Very Long Baseline Interferometry (VLBI) at 1.3 mm (230 GHz) – to resolve the innermost jet of 3C 279 in order to study its fine-scale morphology close to the jet base where highly variable γ-ray emission is thought to originate, according to various models. The source was observed during four days in April 2017 with the Event Horizon Telescope at 230 GHz, including the phased Atacama Large Millimeter/submillimeter Array (ALMA), at an angular resolution of ∼20 μas (at a redshift of z = 0.536 this corresponds to ∼0.13 pc ∼ 1700 Schwarzschild radii with a black hole mass MBH = 8 × 108 M⊙). Imaging and model-fitting techniques were applied to the data to parameterize the fine-scale source structure and its variation. We find a multicomponent inner jet morphology with the northernmost component elongated perpendicular to the direction of the jet, as imaged at longer wavelengths. The elongated nuclear structure is consistent on all four observing days and across different imaging methods and model-fitting techniques, and therefore appears robust. Owing to its compactness and brightness, we associate the northern nuclear structure as the VLBI “core”. This morphology can be interpreted as either a broad resolved jet base or a spatially bent jet. We also find significant day-to-day variations in the closure phases, which appear most pronounced on the triangles with the longest baselines. Our analysis shows that this variation is related to a systematic change of the source structure. Two inner jet components move non-radially at apparent speeds of ∼15 c and ∼20 c (∼1.3 and ∼1.7 μas day−1, respectively), which more strongly supports the scenario of traveling shocks or instabilities in a bent, possibly rotating jet. The observed apparent speeds are also coincident with the 3C 279 large-scale jet kinematics observed at longer (cm) wavelengths, suggesting no significant jet acceleration between the 1.3 mm core and the outer jet. The intrinsic brightness temperature of the jet components are ≲1010 K, a magnitude or more lower than typical values seen at ≥7 mm wavelengths. The low brightness temperature and morphological complexity suggest that the core region of 3C 279 becomes optically thin at short (mm) wavelengths.

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Section: Kinematic Referencementioning

confidence: 63%

Event Horizon Telescope imaging of the archetypal blazar 3C 279 at an extreme 20 microarcsecond resolution

Kim

Krichbaum²,

Broderick³

et al. 2020

A&A

View full text Add to dashboard Cite

show abstract

“…This is a surprising result, given the fact that the δ were obtained for an observing period prior to RoboPol observations under the assumption of energy equipartition between the magnetic field and the radiating particles (Readhead 1994;Lähteenmäki & Valtaoja 1999). This assumption of equipartition may not hold in all sources (see e.g., Gómez et al 2016;Bruni et al 2017). The Doppler factors have on average 30% random errors as shown by Liodakis & Pavlidou (2015).…”

Section: Jet Parameters Vs Rotation Amplitudementioning

confidence: 98%

RoboPol: connection between optical polarization plane rotations and gamma-ray flares in blazars

Blinov

Pavlidou

Papadakis

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We use results of our 3 year polarimetric monitoring program to investigate the previously suggested connection between rotations of the polarization plane in the optical emission of blazars and their gamma-ray flares in the GeV band. The homogeneous set of 40 rotation events in 24 sources detected by RoboPol is analysed together with the gamma-ray data provided by Fermi-LAT. We confirm that polarization plane rotations are indeed related to the closest gamma-ray flares in blazars and the time lags between these events are consistent with zero. Amplitudes of the rotations are anticorrelated with amplitudes of the gamma-ray flares. This is presumably caused by higher relativistic boosting (higher Doppler factors) in blazars that exhibit smaller amplitude polarization plane rotations. Moreover, the time scales of rotations and flares are marginally correlated.

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“…Within the KSP, several of the brightest and also highly polarised AGN have been observed within the first four RadioAstron observing periods, AO-1, 2, 3 and4, between 2013 and Results of these polarisation observations are reported for 0642+449 in , for BL Lac in Gómez et al (2016) and 0716+714 in Kravchenko et al (2020). Bruni et al (2017) analysed 3C 273 in total intensity in Paper II of the series.…”

Section: Introductionmentioning

confidence: 89%

Probing the innermost regions of AGN jets and their magnetic fields with RadioAstron

Pötzl

Lobanov

Ros

et al. 2021

A&A

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Context. Supermassive black holes in the centres of radio-loud active galactic nuclei (AGN) can produce collimated relativistic outflows (jets). Magnetic fields are thought to play a key role in the formation and collimation of these jets, but the details are much debated. Aims. We study the innermost jet morphology and magnetic field strength in the AGN 3C 345 with an unprecedented resolution using images obtained within the framework of the key science programme on AGN polarisation of the Space VLBI mission RadioAstron. Methods. We observed the flat spectrum radio quasar 3C 345 at 1.6 GHz on 2016 March 30 with RadioAstron and 18 ground-based radio telescopes in full polarisation mode. Results. Our images, in both total intensity and linear polarisation, reveal a complex jet structure at 300 μas angular resolution, corresponding to a projected linear scale of about 2 pc or a few thousand gravitational radii. We identify the synchrotron self-absorbed core at the jet base and find the brightest feature in the jet 1.5 mas downstream of the core. Several polarised components appear in the Space VLBI images that cannot be seen from ground array-only images. Except for the core, the electric vector position angles follow the local jet direction, suggesting a magnetic field perpendicular to the jet. This indicates the presence of plane perpendicular shocks in these regions. Additionally, we infer a minimum brightness temperature at the largest (u, v)-distances of 1.1 × 1012 K in the source frame, which is above the inverse Compton limit and an order of magnitude larger than the equipartition value. This indicates locally efficient injection or re-acceleration of particles in the jet to counter the inverse Compton cooling or the geometry of the jet creates significant changes in the Doppler factor, which has to be > 11 to explain the high brightness temperatures.

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Probing the innermost regions of AGN jets and their magnetic fields with RadioAstron

Cited by 34 publications

References 25 publications

Event Horizon Telescope imaging of the archetypal blazar 3C 279 at an extreme 20 microarcsecond resolution

Event Horizon Telescope imaging of the archetypal blazar 3C 279 at an extreme 20 microarcsecond resolution

RoboPol: connection between optical polarization plane rotations and gamma-ray flares in blazars

Probing the innermost regions of AGN jets and their magnetic fields with RadioAstron

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