EDP Sciences
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Volume 482, Number 2, May I 2008
Page(s) 473 - 482
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20077958
Published online 14 February 2008

A&A 482, 473-482 (2008)
DOI: 10.1051/0004-6361:20077958

The role of viscosity in AGN outflows in relation to jet periodicities

G. Lanzafame1, P. Cassaro2, F. Schilliró2, V. Costa3, G. Belvedere4, and R. A. Zappalá4

1  INAF - Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy
    e-mail: glanzafame@oact.inaf.it
2  INAF - Istituto di Radioastronomia, contrada Renna Bassa, CP 161, 96017 Noto (SR), Italy
3  Dipartimento di Metologie Fisiche e Chimiche per l'Ingegneria dell'Universitá, Viale A. Doria 6, 95125 Catania, Italy
4  Dipartimento di Fisica e Astronomia dell'Universitá, Sezione Astrofisica, via S. Sofia 78, 95123 Catania, Italy

(Received 28 May 2007 / Accepted 24 January 2008)

Aims. Adopting the Smoothed Particle Hydrodynamics (SPH) numerical method, we performed a grid of evolving models of a 3D axially-symmetric, viscous accretion disc around a supermassive black hole (SMBH) of $10^{6}\div 10^{9}~ M_{\odot}$. Such sort of simulations are typical of accretion discs in active galactic nuclei (AGN). In such disc models, we pay attention to the role of the specific angular momentum $\lambda$ and the turbulent viscosity parameter $\alpha$, according to the Shakura and Sunyaev prescription. One or two shock fronts in the radial inviscid flow develop, according to the assigned initial kinematic and thermodynamic conditions.
Methods. By fixing the initial and boundary conditions on the flow at the disc outer edge, where the total energy, the specific angular momentum $\lambda$, and the initial velocity are concerned, we find pairs of ($\alpha$, $\lambda$) values determining radial periodical oscillations in the shock front. In some cases, an outflow develops from the subsonic post-shock region, close to the black hole.
Results. The link between the accretion disc and the jet refueling through the onset of a centrifugal shock front is evident. We also compare model variability periods with observed ones in the radio light curves of AGN.

Key words: accretion, accretion disks -- galaxies: active -- shock waves -- galaxies: BL Lacertae objects: general -- galaxies: jets -- hydrodynamics

© ESO 2008

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