NGC 4258: A jet-dominated low-luminosity AGN?

Yuan, Feng; Markoff, Sera; Falcke, H.; Biermann, P. L.

doi:10.1051/0004-6361:20020817

Cited by 86 publications

(90 citation statements)

References 64 publications

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“…The large-scale radio and Hα features of NGC 4258 could only be interpreted as jets (Falcke & Biermann 1999;Yuan et al 2002) after the accretion disk around a super-massive central object had been discovered from observations of water-maser emission (Claussen et al 1984;Henkel et al 1984). Previously they were called "anomalous arms" and explained in terms of ejected matter that interacts strongly with the disk gas and hence is compressed (van der Kruit et al 1972) or as jet-like outflows (Sanders et al 1982).…”

Section: Discussionmentioning

confidence: 99%

The magnetic field along the jets of NGC 4258

Krause

Lohr

2004

A&A

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Abstract. We present 2. 4 resolution, high sensitivity radio continuum observations of the nearby spiral galaxy NGC 4258 in total intensity and linear polarization obtained with the Very Large Array at λ3.6 cm (8.44 GHz). The radio emission along the northern jet and the center of the galaxy is polarized and allows investigation of the magnetic field. Assuming energy-equipartition between the magnetic field and the relativistic particles and distinguishing between (1) a relativistic electron-proton jet and (2) a relativistic electron-positron jet, we obtain average magnetic field strengths of about (1) 310 µG and (2) 90 µG. The rotation measure is determined to range from −400 to −800 rad/m 2 in the northern jet. Correcting the observed E-vectors of polarized intensity for Faraday rotation, the magnetic field along the jet turns out to be orientated mainly along the jet axis. An observed tilt with respect to the jet axis may indicate also a toroidal magnetic field component or a slightly helical magnetic field around the northern jet.

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Section: Discussionmentioning

confidence: 99%

The magnetic field along the jets of NGC 4258

Krause

Lohr

2004

A&A

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“…We here consider one commonly invoked model in which a standard thin, optically thick disk (SD) (Shakura & Sunyaev 1973) exists down to some transition radius r tr , at which point the flow becomes hotter, optically thin and relatively non-radiative (e.g., Esin et al 1997). This type of non-radiative inner disk has also been invoked for lowluminosity AGN such as NGC 4258 (Yuan et al 2002). The thermal bump -seen in several of the GX 339−4 data sets in the optical band -is assumed to originate in the disk, which also provides seed photons for jet IC as mentioned above.…”

Section: Modelmentioning

confidence: 99%

Exploring the role of jets in the radio/X-ray correlations of GX 339-4

Markoff

Nowak

Corbel

et al. 2002

A&A

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262

341

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Abstract. The Galactic black hole candidate X-ray binary GX 339−4 spends most of its time in the low/hard state, making it an ideal candidate for modeling the assumedly low accretion phase. The radio emission correlates very tightly with the X-rays over more than two orders of magnitude in X-ray flux density, suggesting that the jet plasma also plays a role at the higher frequencies. We compare the predictions of our jet model, with and without acceleration, to thirteen broadband simultaneous or quasi-simultaneous spectra over this changing flux history. In addition, we consider a simple standard thin disk which transitions to an optically thin accretion flow, in order to account for the assumedly thermal optical data seen in some observations. A solution without acceleration cannot describe the data without unrealistic energy requirements, nor explain the non-thermal radio spectrum seen during recent radio outbursts. But because of the low disk luminosity, and possibly the assumed disk geometry, acceleration in the jet is limited only by synchrotron cooling and can extend easily into the X-rays. We present a model which can account for all the broadband spectra included here, by changing only two parameters in the jet model: the input power and the location of the first acceleration zone. However, the model is most sensitive to changes in the jet power, the varying of which can also account for the slope of the observed radio/X-ray correlation analytically. At the highest low/hard state luminosities, the synchrotron self-Compton emission from the jet could be detectable with missions such as GLAST, providing a way to test the extent of the synchrotron contribution. We conclude that jet synchrotron is a possible way to explain the broadband features and this correlation, and discuss ways of incorporating this component into the "standard" corona picture.

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“…The RIAF itself efficiently produces radio emission while simultaneously lacking the optical-ultraviolet thermal emission from the standard accretion disk, which acts to boost R (Rees et al 1982;Quataert et al 1999;Ho et al 2000;Ho 2002). At the same time, it has been shown in many cases that a RIAF alone cannot account for all of the observed radio emission, suggesting that an additional radio-emitting component, most likely associated with a jet, is required (Yi & Boughn 1999;Ulvestad & Ho 2001b;Yuan et al 2002;Anderson et al 2004;Falcke et al 2004). On the opposite extreme, NLS1s, probably high-L bol /L Edd systems as discussed above, are systematically radio-quiet (although radio-loud quasars are exceptions; see below).…”

Section: Physical Interpretationmentioning

confidence: 99%

The Radio Quiescence of Active Galaxies with High Accretion Rates

Greene

Ulvestad

2006

ApJ

106

110

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We present 6 cm Very Large Array observations of the Greene & Ho (2004) sample of 19 low-mass active galaxies with high accretion rates. This is one of the only studies of a uniform sample of narrow-line Seyfert 1 (NLS1) galaxies with such high sensitivity and resolution. Although we detect only one source, the entire sample is very radio-quiet down to strong limits. GH10 was found to have a radio power of 8.5 ×10 21 W Hz −1 , and a ratio R ≡ f 6cm / f 4400 of 2.8. The 3 σ upper limits for the remaining nondetections correspond to radio powers from 3 × 10 20 to 8 × 10 21 W Hz −1 and 0.47 < R < 9.9. Stacking all nondetections yields an even stronger upper limit of R ≤ 0.27. An assessment of existing observations in the literature confirms our finding that NLS1s are consistently radio-quiet, with a radio-loud fraction of 0%-6%, which is significantly lower than the 10%-20% observed in the general quasar population. By analogy with stellar-mass black holes, we argue that AGNs undergo a state transition at L bol /L Edd ≈ 0.01. Below this value a radiatively inefficient accretion flow effectively drives an outflow, which disappears when the flow turns into an optically thick, geometrically thin disk, or a radiation pressure-dominated slim disk at still higher L bol /L Edd .

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NGC 4258: A jet-dominated low-luminosity AGN?

Cited by 86 publications

References 64 publications

The magnetic field along the jets of NGC 4258

The magnetic field along the jets of NGC 4258

Exploring the role of jets in the radio/X-ray correlations of GX 339-4

The Radio Quiescence of Active Galaxies with High Accretion Rates

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