- The radio counter-jet of the QSO 3C 48
We present multi-frequency radio observational results of the quasar 3C 48.
The observations were carried out with the Very Large Array (VLA) at five
frequencies, 0.33, 1.5, 4.8, 8.4, and 22.5 GHz, and with the Multi-Element
Radio Linked Interferometer Network (MERLIN) at the two frequencies of 1.6
and 5 GHz. The source shows a one-sided jet to the north within 1", which
then extends to the northeast and becomes diffuse. Two bright components
(N2 and N3), containing most of the flux density, are present in the northern
jet. The spectral index of the two components is alphaN2 ~
-0.99+/-0.12 and alphaN3~-0.84+/-0.23 (S~freqalpha).
Our images show the presence of an extended structure surrounding component N2,
suggestive of strong interaction
between the jet and the interstellar medium (ISM) of the host galaxy. A
steep-spectrum component, labelled S, located 0.25" southwest to the
flat-spectrum component which could be the core of 3C 48, is detected
at a significance of >15sigma. Both the location and the steepness of
the spectrum of component S suggest the presence of a counter-jet in 3C 48.
Feng, W. X.; An, T.; Hong, X. Y.; Zhao, Jun-Hui; Venturi, T.; Shen, Z.-Q.; Wang, W. H., 2005,
AA, 434, 101
- Radio structure of the blazar 1156+295 with sub-pc resolution
1156+295 is a flat-spectrum quasar which is loud at radio and gamma-ray.
Previous observations of the source revealed a radio morphology on pc to kpc
scales consistent with a helical jet model. In our present research,
this source was observed with the VLBA at 86, 43 and 15 GHz at four epochs
from 10 May 2003 to 13 March 2005 aiming at studying the structure of the innermost
jet in order to understand the relation between the helical structure and the astrophysical
processes in the central engine. A core-jet structure with six jet components is identified.
The apparent transverse velocities of the six jet components derived from proper motion
measurements are in the range between 3.6 c and 11.6 c. The overall jet shape shows
oscillatory morphology with multiple curvatures on pc scales which might be
indicative of a helical pattern. Models of helical jet are discussed on the basis of
both Kelvin-Helmholtz (K-H) instability and jet precession. The K-H instability
model shows better agreement with the observed data. The overall radio structure
on the scale from sub-pc to kpc appears to be fitted with a hydrodynamic model with
the fundamental helical mode in Kelvin-Helmholtz (K-H) instability. This helical mode
with an initial characteristic wavelength of 0.2 pc is excited at the base of the jet
on the scale of 0.005 pc (or 1000Rs, the typical size of the broad line region
for a super massive black hole of 4.3x108 Mo). A presessing jet
model can also fit the observed jet structure on the scale between 10 pc and 300 pc.
However, additional astrophysical processes may be required for the presessing jet model
in order to explain the bendings on the inner jet structure (1 to 10 pc) and re-collimation
of the large scale jet outflow (>300 pc).
W. ZHao; Hong, X. Y.; An, T.; Zhao, Jun-Hui; Gurvits, L. I.; Yang, J., 2011,
AA, 529, 113