Sub-Parsec-Scale Acceleration of the Radio Jet in the Powerful Radio Galaxy NGC 6251

Sudou, Hiroshi; Taniguchi, Yoshiaki; Ohyama, Youichi; Kameno, Seiji; Sawada-Satoh, Satoko; Inoue, Makoto; Kaburaki, Osamu; Sasao, Tetsuo

doi:10.1093/pasj/52.6.989

Cited by 29 publications

(39 citation statements)

References 16 publications

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“…4. DISCUSSION Sudou et al (2001) see a very short (%1 mas) counterjet in their VLBI images of NGC 6251 at 5 and 15 GHz. Our 5.0 GHz image also shows a possible short extension in the counterjet direction from the brightest peak, but we do not consider this a reliable feature because of its faintness and the fact that its extent is no greater than one beamwidth.…”

Section: Resultsmentioning

confidence: 89%

“…Our 5.0 GHz image also shows a possible short extension in the counterjet direction from the brightest peak, but we do not consider this a reliable feature because of its faintness and the fact that its extent is no greater than one beamwidth. Note that our angular resolution at 5 GHz is not as good as that of Sudou et al (2001), who had data from the Highly Advanced Laboratory for Communications and Astronomy (HALCA) spacecraft of the VSOP mission in addition to their ground-based VLBI array. The counterjet in Sudou et al's (2001) 5 GHz image appears at an unexpected position angle (not parallel to the main jet) and only at the higher resolution provided by the HALCA data.…”

Section: Resultsmentioning

confidence: 97%

“…Note that our angular resolution at 5 GHz is not as good as that of Sudou et al (2001), who had data from the Highly Advanced Laboratory for Communications and Astronomy (HALCA) spacecraft of the VSOP mission in addition to their ground-based VLBI array. The counterjet in Sudou et al's (2001) 5 GHz image appears at an unexpected position angle (not parallel to the main jet) and only at the higher resolution provided by the HALCA data. We do not see any flux along the position angle of the Sudou et al (2001) counterjet in our lower resolution but higher dynamic range image at 5.0 GHz.…”

Section: Resultsmentioning

confidence: 97%

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What Happened to the NGC 6251 Counterjet?

Jones

Wehrle

2002

ApJ

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We have used the Very Long Baseline Array to produce a high dynamic range image of the nucleus of NGC 6251 at 1.6 GHz and snapshot images at 5.0, 8.4, and 15.3 GHz to search for emission from a parsecscale counterjet. Previous VLBI images at 1.6 GHz have set a lower limit for the jet/counterjet brightness ratio near the core at about 80:1, which is larger than expected, given the evidence that the radio axis is fairly close to the plane of the sky. A possible explanation is that the inner few parsecs of the counterjet are hidden by free-free absorption by ionized gas associated with an accretion disk or torus. This would be consistent with the nearly edge-on appearance of the arcsecond-scale dust disk seen in the center of NGC 6251 by Hubble Space Telescope (HST). We detect counterjet emission close to the core at 1.6 GHz, but not at the higher frequencies. Given that the optical depth of free-free absorption falls off more rapidly with increasing frequency than the optically thin synchrotron emission from a typical radio jet, this result implies that the absence of a detectable parsec-scale counterjet at high frequencies is not due to free-free absorption unless the density of ionized gas is extremely high and we have misidentified the core at 1.6 GHz. The most likely alternative is a large jet/counterjet brightness ratio caused by relativistic beaming, which in turn requires the inner radio axis to be closer to our line of sight than the orientation of the HST dust disk would suggest.

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Section: Resultsmentioning

confidence: 89%

Section: Resultsmentioning

confidence: 97%

Section: Resultsmentioning

confidence: 97%

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What Happened to the NGC 6251 Counterjet?

Jones

Wehrle

2002

ApJ

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“…In NGC 315 found an increasing jet velocity in the 5 inner pc from the core both from proper motion measurements AND from the sidedness ratio. Recently an increasing bulk velocity has been found also in NGC 6251 by Sudou et al (2000). In many low power sources there are observational evidences (Laing et al 2003) that jets are relativistics at their beginning and strongly decelerate within a few kpc from the core (see e.g.…”

Section: Acceleration and Deceleration In Jetsmentioning

confidence: 93%

Observational Properties of Jets in Active Galactic Nuclei

Giovannini

2004

Astrophysics and Space Science

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“…Its kiloparsec-scale radio emission has been investigated in great detail using the Very Large Array (VLA) (Perley et al 1984), and the parsec-scale jet emission using VLBI continuously extending to 50 mas (Jones et al 1986;Sudou et al 2000;Jones & Wehrle 2002). The mass of the SMBH is measured to be M = (6 ± 2) × 10 8 M (Ferrarese & Ford 1999).…”

Section: Introductionmentioning

confidence: 99%

Structural Transition in the NGC 6251 Jet: An Interplay With the Supermassive Black Hole and Its Host Galaxy

Tseng

Asada

Nakamura

et al. 2016

ApJ

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The structure of the NGC 6251 jet on the milliarcsecond scale is investigated using images taken with the European VLBI Network and the Very Long Baseline Array. We detect a structural transition of the jet from a parabolic to a conical shape at a distance of (1 − 2) × 10 5 times the Schwarzschild radius from the central engine, which is close to the sphere of gravitational influence of the supermassive black hole (SMBH). We also examine the jet pressure profiles with the synchrotron minimum energy assumption to discuss the physical origin of the structural transition. The NGC 6251 jet, together with the M87 jet, suggests a fundamental process of the structural transition in the jets of active galactic nuclei (AGNs). Collimated AGN jets are characterized by their external galactic medium, showing that AGN jets interplay with the SMBH and its host galaxy.

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Sub-Parsec-Scale Acceleration of the Radio Jet in the Powerful Radio Galaxy NGC 6251

Cited by 29 publications

References 16 publications

What Happened to the NGC 6251 Counterjet?

What Happened to the NGC 6251 Counterjet?

Observational Properties of Jets in Active Galactic Nuclei

Structural Transition in the NGC 6251 Jet: An Interplay With the Supermassive Black Hole and Its Host Galaxy

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