The Small-Scale Structure of Radio Galaxies and Quasi-Stellar Sources at 3.8 Centimeters

Cohen, M. H.; Cannon, Walter F.; Purcell, G. H.; Shaffer, D. B.; Broderick, J. J.; Kellermann, K. I.; Jauncey, D. L.

doi:10.1086/151204

Cited by 152 publications

(87 citation statements)

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“…The FSRQ 3C 279 (α2000.0 = 12h 56m 11.17s, δ2000.0 = −05 • 47 ′ 21.5 ′′ ) at a redshift of 0.536 (Burbidge & Rosenburg 1965) was the first extragalactic radio source indicating superluminal motion (Cohen et al 1971). It displays violent multiwavelength flux variability and is well studied by various observation programs (e.g.…”

Section: C 279mentioning

confidence: 99%

Core shift effect in blazars

Agarwal

Mohan

Gupta

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We studied the pc-scale core shift effect using radio light curves for three blazars, S5 0716+714, 3C 279 and BL Lacertae, which were monitored at five frequencies (ν) between 4.8 GHz and 36.8 GHz using the University of Michigan Radio Astronomical Observatory (UMRAO), the Crimean Astrophysical Observatory (CrAO), and Metsahovi Radio Observatory for over 40 years. Flares were Gaussian fitted to derive time delays between observed frequencies for each flare (∆t), peak amplitude (A), and their half width. Using A ∝ ν α we infer α in the range −16.67 to 2.41 and using ∆t ∝ ν 1/kr , we infer k r ∼ 1, employed in the context of equipartition between magnetic and kinetic energy density for parameter estimation. From the estimated core position offset (Ω rν ) and the core radius (r core ), we infer that opacity model may not be valid in all cases. The mean magnetic field strength at 1 pc (B 1 ) and at the core (B core ), are in agreement with previous estimates. We apply the magnetically arrested disk model to estimate black hole spins in the range 0.15 − 0.9 for these blazars, indicating that the model is consistent with expected accretion mode in such sources. The power law shaped power spectral density has slopes −1.3 to −2.3 and is interpreted in terms of multiple shocks or magnetic instabilities.

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Section: C 279mentioning

confidence: 99%

Core shift effect in blazars

Agarwal

Mohan

Gupta

et al. 2017

Monthly Notices of the Royal Astronomical Society

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“…The first evidence of this goes back to the 1960s with the interpretation of brightness temperatures of quasar radio emission exceeding the Compton limit by Rees (1966). This was beautifully confirmed by the observation of superluminal motions with the achievement of the very long base interferometry (VLBI) technique (Cohen et al 1971). These superluminal events are only possible for actual speeds larger than 0.7c.…”

Section: Introductionmentioning

confidence: 85%

Variation of bulk Lorentz factor in AGN jets due to Compton rocket in a complex photon field

Vuillaume

Henri

Petrucci

2015

A&A

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Radio-loud active galactic nuclei are among the most powerful objects in the universe. In these objects, most of the emission comes from relativistic jets getting their power from the accretion of matter onto supermassive black holes. However, despite the number of studies, a jet's acceleration to relativistic speeds is still poorly understood. It is widely known that jets contain relativistic particles that emit radiation through several physical processes, one of them being the inverse Compton scattering of photons coming from external sources. In the case of a plasma composed of electrons and positrons continuously heated by the turbulence, inverse Compton scattering can lead to relativistic bulk motions through the Compton rocket effect. We investigate this process and compute the resulting bulk Lorentz factor in the complex photon field of an AGN composed of several external photon sources. We consider various sources: the accretion disk, the dusty torus, and the broad line region. We take their geometry and anisotropy carefully into account in order to numerically compute the bulk Lorentz factor of the jet at every altitude. The study, made for a broad range of parameters, shows interesting and unexpected behaviors of the bulk Lorentz factor, exhibiting acceleration and deceleration zones in the jet. We investigate the patterns of the bulk Lorentz factor along the jet depending on the source sizes and on the observation angle and we finally show that these patterns can induce variability in the AGN emission with timescales going from hours to months.

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“…Most observed sources exhibit spatially extended structures that are variable in both time and frequency. The structure and kinematics of compact extragalactic radio sources have been the subject of astrophysical studies since their discovery more than four decades ago (Cohen et al 1971;Knight et al 1971;Whitney et al 1971). Currently, some geodetic sources have a long history of structure evolution monitoring with high spatial resolution (e.g.…”

Section: Introductionmentioning

confidence: 99%

On the estimation of a celestial reference frame in the presence of source structure

Plank

Shabala

McCallum

et al. 2015

Mon. Not. R. Astron. Soc.

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The spatial structure of sources making up the celestial reference frame (CRF) at radio frequencies is a systematic error source in very long baseline interferometry (VLBI) measurements. Using simulations, we investigate the effects of source structure on the CRF, determined by the actual observational programme of the International VLBI Service for Geodesy and Astrometry. This is done using the source structure simulator of the Vienna VLBI Software. Applying various mock two-component source models, systematic displacements of 10-80 μas in median source position offsets are found. These offsets are predominantly aligned with the direction of the jet. The simulations further show that slight changes in the source model can significantly change the estimated positions. We finally present a new parametrization of source positions in the analysis, namely along the jet direction and perpendicular to it, allowing us to significantly mitigate the effects of source structure on an estimated CRF.

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The Small-Scale Structure of Radio Galaxies and Quasi-Stellar Sources at 3.8 Centimeters

Cited by 152 publications

References 0 publications

Core shift effect in blazars

Core shift effect in blazars

Variation of bulk Lorentz factor in AGN jets due to Compton rocket in a complex photon field

On the estimation of a celestial reference frame in the presence of source structure

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