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    {\small\rm\zihao{6}\songti\thepage\hfill
    \quad\quad ACTA ASTRONOMICA SINICA \hfill
    \hspace{2mm} Vol.44\vspace{2mm}}}} %%%%%%%
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    {\small\rm \zihao{6}\songti suppl.\hfill W. H. Wang et al.: Radio Structure of
    the Quasar 0202+149 on Subarcsecond Scale  %%（作者：题目名称）
    \vspace{1.5mm}
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    \normalsize\rm
\zihao{5}\songti

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    Vol.44~ Suppl.
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    \small ACTA ASTRONOMICA SINICA
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      Feb.,~2003 \\[-1.5 true mm] %%January
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\vs\vs\vs \bc {\Large\bf Radio Structure of the Quasar 0202+149\\[2mm] on Subarcsecond Scale    %%（文题）
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\vs\vs{\normalsize\zihao{4}\fangsong W. H. Wang,\hs\hs X. Y. Hong,\hs\hs D. R. Jiang\hs\&\hs T. An}  %%（本文作者）

\vs
(\sho) %%（本文作者单位）
\vs\vs \ec

\normalsize
\begin{quotation}

 \no{\bf A{\scriptsize\bf BSTRACT }}~~~\small
We present the results of MERLIN observations at 5\,GHz and VLBA
observation at 1.67\,GHz for the $\gamma$-ray bright quasar
0202+149. Two images on subarcsecond scales first reveal that
0202+149 contains two mini-lobes separated about ~200\,mas,
located on both sides of a bright radio core. The northeast lobe
is resolved into two hot knots by the VLBA observation. Combining
multiepoch multifrequency VLBI images, we investigate the spatial
evolution of the radio jet on scales from 0.5\,mas to 0.5
arcsecond. The $\gamma$-ray quasar 0202+149 maybe be the first
superluminal source with two-sided jet structure on subkiloparsec
scale. We rule out the possibility that 0202+149 is a Compact
Symmetric Object (CSO). We prefer 0202+149 has stronger bent jet
structure on scales from parsec to subkiloparsec rather than a
compact F doubles.


\vn
 \no{\bf Key words}~~  pulsar-mode  change-spectrum
\end{quotation}

%%%% 正文
 \para{\large\bf{1}~~ Introduction}

\vs\vs The source 0202+149 (J0204+1514, 4C +15.05) is a
flat-spectrum quasar with redshift $z=0.833$ (Herbig \& ReadHead
1992; Stickel et al. 1996). It was detected by EGRET as a
$\gamma$-ray source (von Montigny et al. 1995) and identified as a
variable source with a high level of probability in the second
EGRET catalog (Mattox et al. 1997). However, unlike general
$\gamma$-ray sources, 0202+149 has little radio variability (Piner
\& Kingham 1998) and low radio polarization (Perley 1982).

The $\gamma$-ray quasar 0202+149 has been observed and imaged in
the radio band. A VLA observation at 1.4\,GHz presented an
unresolved component on the kpc scale (Perley 1982; also see
Murphy et al. 1993). Higher resolution observations showed that
0202+149 is a core-dominated structure with a faint jet in the
northwest direction on pc scale and the jet component is
stationary (Bondi et al. 1996; Piner \& Kingham 1998; Pyatunina et
al. 2000). A 22\,GHz VLBI observation (Moellenbrock et al. 1996)
measured a brightness temperature of 0202+149 in excess of the
inverse Compton limit ($10^{12} K$) for synchrotron radiation,
indicating the likelihood of relativistic beaming in this source.
43\,GHz VLBA observations (Pyatunina et al. 2000) revealed a inner
bent jet and proposed a proper motion of $0.18\pm0.01$ mas/yr,
corresponding to an apparent superluminal velocity $(8.1\pm0.3)c$
(where $q_0=0.1$, $H_0=65$\,km\,s$^{-1}$Mpc$^{-1}$).

In this paper, we will present the results obtained from MERLIN
observations at 5\,GHz, VLBA observation at low frequency of
1.67\,GHz. We investigate the spatial evolution of 0202+149 on
scales from 0.5\,mas to 0.5 arcsecond.

 \newpage
 \vspace*{1mm}\para{\large\bf{2}~~ Observations and the results}

\vs\vs The $\gamma$-ray bright quasar 0202+149 was observed with
MERLIN on 12th Nov 1998. The participating antennas of MERLIN are
Cambridge, Darnhall, Defford, Tabley and Knockin, but the antenna
Tabley was failed in the observation. The source was also observed
with Very Long Baseline Array (VLBA) as a part of a EGRET-detected
AGNs monitoring campaign (Hong et al. in preparation) on 17th Feb
2000 at wavelength of 18 cm (1.67\,GHz) in ``snapshot'' mode. The
primary data reduction of the VLBA data were done in the NRAO
Astronomical Imaging Processing Software (AIPS) package (Cotton
1995; Diamond 1995). For MERLIN data, the amplitude calibration
was done with d program by Dr. Garringtonin in Jodrell bank
observatory. The imaging of 2 epochs data were performed with AIPS
or the package DIFMAP (Shepherd et al. 1994).

The MERLIN image at 5\,GHz and the VLBA image at 1.67\,GHz are
displayed in Figure 1.

\begin{figure}[h]

\center {\includegraphics [bb= 0 0 357 158,scale=1]{w1.eps}}

   \parbox[tb]{13cm}
   %{\hspace{3.5cm}
   {%\center

  \vspace{2mm} \footnotesize

      Fig.\,1~~ Left: the MERLIN Image at
5~GHz on epoch 1998.87. Contour peak flux =2.31\,Jy/beam.
Levs=6\,mJy/beam $\times$ (-1, 1, 2, 4, 8, 16, 32, 64, 128, 256),
Beam FWHM: 110 $\times$ 37.2 mas at 16$\deg$. Right: the VLBI
image with VLBA at 1.67\,GHz on epoch 2000.10. Contour peak flux
=1.22\,Jy/beam. Levs=3.7\,mJy/beam $\times$ (-1, 1, 2, 4, 8, 16,
32, 64), Beam FWHM: 10 $\times$ 4.99\,mas at 1.27$\deg$.}

    \end{figure}

\para{\large\bf{3}~~ Morphology and Structural Evolution}

\vs\vs Both MERLIN and VLBA images exhibited that the source
0202+149 has extended mini-lobes straddling the core. In the
MERLIN image, the core component was labelled C and the extended
mini-lobes were labelled E and F respectively (See the left in
Figure 1.). Two other components were detected. The component E
was resolved with two hot spots labelled E1 and E2 in the VLBA
image (See the right of Figure 1). In fact, Bondi et at. (1996)
found the VLBI map accounts only for  50\% of the flux density
measured by the Effelsberg 100\,m telescope and predicted that
there must be an extended component on a scale of hundreds of mas.
Our results confirm the prediction. Moreover, the results show
that 0202+149 clearly has an extended component on the other side
of the core. Our observations first reveal that the $\gamma$-ray
quasar 0202+149 contained with symmetric mini-lobes straddling the
bright core on subarcsecond scale.

On the basis of the results and the previous publications (Bondi
et al. 1996; Murphy et al. 1993; Perley 1982; Piner \& Kingham
1998; Pyatunina et al. 2000), we can investigate the spatial
evolution of the radio jet of 0202+149 from small scale to large
scale. The redshift of 0202+149 indicated the source located at a
distance of  100\,Mpc (so 1\,mas $\sim$ 3.6\,pc). The morphology
features of 0202+149 includes the followings:

(1) Multiepoch VLBA observations at 43\,GHz clearly showed the jet
structure of the inner ($r<1$\,mas) region of 0202+149, suggesting
either strong curvature or complex cross-sectional structure
(Pyatunina et al. 2000). Based on 4 epochs high resolution 43\,GHz
VLBA images, Pyatunina et al. (2000) revealed the superluminal
motion of component of the inner jet with an apparent superluminal
velocity $(8.1\pm0.3)c$. This is consistent with that the
$\gamma$-ray sources are strongly beamed (von Montigny et al.
1995).

(2) The VLBI observations on mas scale revealed a core-dominated
structure with a diffuse jet out to $\sim$ 7\,mas (Bondi et al.
1996; Pyatunina et al. 2000; Piner \& Kingham 1998). The outer jet
structure ($r<10$\,mas) showed that the extended jet component at
a distance $\sim$ 5\,mas and PA $\sim$ 60 $\deg$ is stationary.

(3) The MERLIN and VLBA observation in this paper revealed the
triple jet structure on the intermediate scale ($r<0.5$
arcsecond). The two components on either side of the bright core
are probably mini-lobes. And the two mini-lobes have similar flux
density.

(4) 0202+149 was unresolved on scales greater than 1\,kpc (Perley
1982; Murphy et al. 1993).

\para{\large\bf{4}~~ Discussion and Conclusions}

\vs\vs Figure 1 shows that 0202+149 has the outer mini-lobes
separated by 720 pc, straddling the core. Considering compactness
of 0202+149 on kpc scale, we easily think that it is a CSO
(Pearson \& Readhead 1988; Conway et al. 1994). The $\gamma$-rays
loud emission of 0202+149 imply that the source is strongly beamed
(von Montigny et al. 1995). Pyatunina et al. (2000) has also
detected the superluminal motion on pc scale for 0202+149. This
contrasts with the radio properties of CSOs in which relativistic
beaming does not play a major role (Wilkinson et al. 1994).
Moreover, the flux density of the core at low frequency should be
weaker for CSOs. From Figure 1 and 2, the core of 0202+149 is
obviously brighter than mini-lobes. So we don't think that the
source 0202+149 is a CSO.

Piner \& Kingham (1998) suggested 0202+149 as a new compact F
double source. The reasons included (1) 0202+149 contains with a
resolved core and a stationary extended jet component on mas
scale; (2) little or no radio variability; (3) no detectable
structure on the scale of kpc. Conway et al (1994) indicated that
the compact F doubles generally show flatter high-frequency
spectra and are associated with an apparently one-sided radio jet.
However the MERLIN and VLBA images show that 0202+149 have
two-sided radio jets on subkpc scale. We need more evidence and
the spectral information to decide whether 0202+149 can be
classified as a compact F doubles.

The phenomena of the $\gamma$-ray emission and the superluminal
motion show that 0202+149 is relativistic beamed. This means that
the jet components are very close to the line of sight. Because of
relativistic beaming, the counter-jets are not visible on the mas
scale. This is consistent with the structure on the pc scale. The
triple structure on subarcsecond implies that 0202+149 might have
two-sided radio jets structure. This suggests that the direction
of the jet components is strongly changed from pc scales to subkpc
scales. So both advancing and receding jets could still be visible
on subkpc scale. But it is difficult to decide how the pc scale
jet is connected to the mini-lobes on subarcsecond scale. Lacking
of the obvious evidence connecting the jet component on pc scale
to subkpc scale, we cannot rule out that the mini-lobes are the
jet components previously ejected from the core.

In this paper we have reported an ongoing work aimed to
investigate the spatial evolution of the radio jets of 0202+149 on
scales from submas to subarcsecond. The $\gamma$-ray quasar
0202+149 maybe be the first superluminal source with two-sided jet
structure on subkiloparsec scale. We also suggest that the
$\gamma$-ray quasar 0202+149 tend to have strong bent-jet
structure on scales from pc to sub-kpc.

\vs\vn{\bf ACKNOWLEDGEMENTS}~~ This research was supported by the
National Natural Science Foundation of China, Foundation of
Chinese Academy of Sciences (19973103), and Pan Deng Plan of
China. WWH thanks Dr Leonid Gurvits for help during his visit the
Netherlands for the data reduction in 2001. This work has made use
of NASA's Astrophysics Data System Abstract Service.

\bc {\bf References} \ec

\vspace{-4mm} \no \fns

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\end{CJK}
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