1,792 research outputs found
On the nature of an ejection event in the jet of 3C111
We present a possible scenario for the ejection of a superluminal component
in the jet of the Broad Line Radio Galaxy 3C111 in early 1996. VLBI
observations at 15 GHz discovered the presence of two jet features on scales
smaller than one parsec. The first component evolves downstream, whereas the
second one fades out after 1 parsec. We propose the injection of a perturbation
of dense material followed by a decrease in the injection rate of material in
the jet as a plausible explanation. This scenario is supported by 1D
relativistic hydrodynamics and emission simulations. The perturbation is
modeled as an increase in the jet density, without modifying the original
Lorentz factor in the initial conditions. We show that an increase of the
Lorentz factor in the material of the perturbation fails to reproduce the
observed evolution of this flare. We are able to estimate the lifetime of the
ejection event in 3C111 to be 36\pm7 days.Comment: Accepted for publication in Astronomy & Astrophysics Letter
Radio-optical scrutiny of the central engine in compact AGN
We combine Very-Long-Baseline Interferometry (VLBI) data for active
galactic nuclei (AGN) available from the Very Large Baseline Array (VLBA) 2 cm
imaging survey and optical spectroscopy to investigate the relationships in the
emission-line region--central engine--radio jet system. Here, we present the
diversity of spectral types among the brightest AGN in our sample. We also
discuss correlations between the mass of the central engine and properties of
the parsec-scale radio jet for 24 AGN selected by the presence of H
broad-emission lines in their spectra.Comment: 4 pages, 5 figures, to appear in the proceedings of the Workshop on
"Multiband Approach to AGN" held in Bonn (Germany), 30 September - 2 October
2004, to be published in "Memorie della Societa Astronomica Italiana
NGC1052 - A study of the pc-scale twin jet
We present results of a VLBA multi-frequency study of the pc-scale twin jet
in NGC1052. We observed this object at epoch 1998.99 with the VLBA at 5, 8.4,
22 and 43 GHz both in total and linearly polarized intensity. The spectral
analysis confirms the necessity of a free-free absorbing medium, obscuring the
innermost part of both jets. At 5 GHz we found a compact linearly polarized
emission region at the base of the eastern jet with a degree of polarization of
1.5%. At higher frequencies there is no evidence for polarization in our data.
A core shift analysis constrains the position of the central engine to ~0.03
pc. The shift rates of the apparent core position with frequency confirm the
strong influence of free-free absorption in conjunction with steep pressure
gradients at the bases of both jets.Comment: Proceedings of the conference "SRT: the impact of large antennas on
Radio Astronomy and Space Science", Cagliari, Italy, 7-10 November 2001, in
press; 6 pages, 5 figures, needs srt_style.st
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