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VLBI observations of the quasar 3C380
By I z a b e l a Ow s i a n i k
e­mail: iza@astro.uni.torun.pl
Torun Radio Observatory, Nicolaus Copernicus University, POLAND
There are result from two global VLBI observations at 3.6 cm spaced about 2 years. These
observations were made in epochs 1989.9 and 1992.25 and they are unique at 8.4 GHz frequency.
The maps were made with 0.5 mas resolution and show dramatic changes in the structure over
the period. The analysis of the apparent motion, indication of the jet flow trajectory and the
other implications for the CSS quasars are discussed.
1. Introduction
The quasar 3C380 (z = 0:692; thus 1 arcsec corresponds to 4 kpc for H 0 = 100
km s \Gamma1 Mpc \Gamma1 , q 0 = 0:5) is one of the most powerful radio sources (its radio luminosity
at 2.7 GHz is P 2:7 GHz ¸ 10 28 W Hz \Gamma1 ) (Wilkinson et al. (1984)). 3C380 is a member
of the class of Compact Steep Spectrum (CSS) sources. CSS objects are those sources,
which are unresolved or barely resolved by conventional interferometry (angular size
¸ 1 0 \Gamma 2 00 ) and have a steep high frequency spectrum (spectral index ff – 0:5, with
S / š \Gammaff ) (Kapahi (1981), Peacock & Wall (1982)). Their occurrence is quite high in
catalogues of radio sources (from 15% to 30%, depending on selection frequency). For
many years they were not studied intensively, because of their uninteresting structure
at arcsec resolution. At resolutions of hundreds to tens of arcsec, CSSs show the same
variety of structure as the more extended radio sources, i.e. double, triple and core--jet
(Fanti et al. (1990)). In addition, very complex structures reminiscent of sharply bent
jets are also observed.
The majority of the powerful steep­spectrum sources have FR II structures (Fanaroff
& Riley (1974)), i.e. two dominant edge­brightened lobes straddling a relatively weak
core. However, 3C380 does not fit to this pattern. Instead it has a relatively strong core,
which dominates the spectrum above ¸ 20 GHz, surrounded by a tangle of emission whose
underlying structure is far from clear (Wilkinson et al. (1984)). 3C380 is classified as
a CSS source despite its extended structure (angular size ú 7 arcsec), since most of its
radio emission at 5 GHz apparently comes from a region only a few arcsec in extent,
which is not typical of FR II sources. Quasar 3C380 shows complex or very asymmetric
structure on the kilo­parsec scale, whereas on the parsec scale it belongs to the one­sided
jet morphology.
2. Observational results
VLBI observations of the quasar 3C380 were made with 8­telescopes on the 19th
November 1989 and with 13­telescopes on the 1st April 1992. Data were correlated in
OVRO Caltech by Dr Faith Austin, then reduced with Astronomical Image Processing
System (AIPS). The maps were made with 0.5 mas resolution and show dramatic changes
in the structure over the period (2.36 yrs).
The detailed comparison of both maps leads to the following conclusions (see Figure
2):
(a) Apparent velocities have been measured on the scale 0:5 \Gamma 22 mas, it ranges from
1

2 Izabela Owsianik: VLBI observations of the quasar 3C380
3C380 IPOL 8417.990 MHZ 3C380.ICLN.2
PLot file version 1 created 17­JUN­1994 14:34:01
Peak flux = 7.6771E­01 JY/BEAM
Levs = 7.6771E­03 * ( ­2.00, ­1.00, 1.000,
2.000, 4.000, 8.000, 16.00, 32.00, 64.00,
128.0, 256.0, 512.0, 1024.)
DECLINATION
(B1950)
RIGHT ASCENSION (B1950)
18 28 13.460 13.459
48 42 41.014
41.012
41.010
41.008
41.006
41.004
41.002
41.000
B
C 2
C 0
C 1
A
F
3C380 IPOL 8417.240 MHZ 3C.ICLN.1
PLot file version 1 created 17­JUN­1994 14:36:18
Peak flux = 7.8652E­01 JY/BEAM
Levs = 7.8652E­03 * ( ­2.00, ­1.00, 1.000,
2.000, 4.000, 8.000, 16.00, 32.00, 64.00,
128.0, 256.0, 512.0, 1024.)
DECLINATION
(B1950)
RIGHT ASCENSION (B1950)
18 28 13.460 13.459
48 42 41.014
41.012
41.010
41.008
41.006
41.004
41.002
41.000
C 2 C 1
C 3
A
B
C 0
F
Figure 1. Global VLBI maps of 3C380 at 8.4 GHz made for epochs 1989.9 and 1992.25.
Contour levels are 0.5, 1, 2, 4, 8, 16, 32, and 64% of the peak brightness (about
0:8 Jy beam \Gamma1 ).
0:26 to 1:05 mas yr \Gamma1 . Component C3 has moved with the same velocity as the com­
ponent A (0:26 mas yr \Gamma1 ).
(b) the PA of the apparent velocity vector changes from \Gamma24 to \Gamma59 degree.
(c) The 8 mas long jet rotates anticlockwise at about 3 deg yr \Gamma1 (measured at the
component C0).
The quasar 3C380 is a very active, very strong and it shows a large range of variability.

Izabela Owsianik: VLBI observations of the quasar 3C380 3
Distance from core [mas]
Apparent
velocity
[mas
/
y]
0
0,2
0,4
0,6
0,8
1
1,2
0 2 4 6 8 10 12 14 16 18 20 22
B
A
F
C1
C3 C2
Figure 2. The apparent velocity for all components of 3C380 derived from maps.
The observed motion is most probably a combination of the ballistic (near the core) and
helical type in the distant regions (Kus et al. (1993)).
3. Discussion
Initial disturbance in the jet direction can account for some of the observed features.
Without the existence of inhomogeneities in the dense and/or turbulent medium it is very
difficult to propose a realistic physical phenomenon which would explain the observed
facts (Readhead (1993)). 3C380 exhibits several features expected of FR II sources seen
approximately end­on, like superluminal motion in the core, the similarity of the NW
knots to double hot spots in FR II lobes and so on. However, not all of 3C380 futures
can be so easily accounted for by projection to the line of sight, in particular the core is
relatively weak and it is not strongly variable at radio and optical wavelengths (Wilkinson
et al. (1991)).
Radio statistics suggest that CSS objects are rather intrinsically small sources of sub­
galactic size. High resolution observations reveal a striking similar radio structure to
that observed in the extended sources, with jets and lobes, and invariably displaying a
flat spectrum radio core at high frequencies. The age of CSS's (10 4 \Gamma 10 6 y) implies that
they are represent a young evolutionary stage of the large radio sources, in which the
radio jets are still propagating through the interstellar medium. Projection and beaming
effects are a possible explanation for the strong cores and jets in CSS quasars, which
also are generally more asymmetric. Asymmetries are probably due to differences in the
density of the ambient medium, and the interaction effects between the radio emitting
plasma and the surrounding medium are likely to dominate the appearance of the ra­
dio structure. Evidence that CSSs inhabit a denser and possibly clumpier medium is
shown by their more misaligned and asymmetric radio structures than are observed in
the extended sources (Sanghera (1992)).
There is strong need to continue the VLBI observations of quasar 3C380 at high
frequency with better sensitivity. More frequent, regular study of structure changes
should provide us with the new information on detailed evolution of the jets and physics
of such phenomena. Our proposal to continue VLBI monitoring of quasar 3C380 was

4 Izabela Owsianik: VLBI observations of the quasar 3C380
accepted, and we hope that it will help us to built up a theory of interaction with the
environment.
I thank all people for proposal of VLBI observations of this quasar. They are R.S.
Booth Onsala Space Observatory, T.J. Pearson and A.C.S. Readhead OVRO Caltech,
P.N. Wilkinson NRAL Jodrell Bank and specially my supervisor A.J. Kus TRAO Torun
for all help.
REFERENCES
Fanaroff B.L., Riley J.M., 1974, MNRAS, 167, 31.
Fanti R., Fanti C., Schilizzi R.T., Nan Rendong, Parma P., van Breugel W.J.M., Venturi T.,
1990, A&A, 231, 333.
Kapahi V.K., 1981, A&AS, 43, 381.
Kus A.J., Booth R.S., Marecki A., Maszkowski R., Porcas R.W., Pearson T.J., Readhead A.C.S.,
Wilkinson P.N., 1993, in Sub­arcsecond Radio Astronomy, eds Davis R.J. & Booth R.S.,
p.222, (Cambridge University Press).
Peacock J.A., Wall J.V., 1982, MNRAS, 198, 843
Readhead A.C.S., 1993, in Sub­arcsecond Radio Astronomy, eds Davis R.J. & Booth R.S., p.173,
(Cambridge University Press).
Sanghera H.S., 1992, PhD thesis, (University of Manchester).
Wilkinson P.N, Booth R.S., Cornwell T.J., Clark R.R., 1984, Nature, 308, 619.
Wilkinson P.N., Chidi E. Akujor, Cornwell T.J., Saikai D.J., 1991, MNRAS, 248, 86 .