| 61. |
- Standke, K. J., et al.
(författare)
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High Sensitivity VLBI at 86 GHz : First Fringes with the 100 m Radio Telescope at Effelsberg
- 1993
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Ingår i: VLBI Technology. - Tokyo : Terra Scientific. - 4887041128 ; , s. 75-85
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Bokkapitel (refereegranskat)abstract
- Inclusion of large and sensitive antennas is of essential importance to further improve the imaging capabilities of VLBI at 3.5 mm wavelength. The combination of the 100 m radio telescope at Effelsberg (illuminated diameter ~60 m at lambda = 3.5 mm) with the 30 m radio telescope at Pico Veleta presently allows the detection of compact flux down to a level of 0.2 Jy (for τ=360 seconds integration time). Fringes have been found for 23 radio sources many of them not observed previously with VLBI at 86 GHz. On European baselines to Effelsberg the SNR typically was 10 to 30 (and ranged up to 107 for 3C279), facilitating model fitting for the brightest sources. Even in spite of chaning weather conditions during the observations (coherence times ranged between 10 to 100 seconds) and a still non-optimum pointing model for the 100 m antenna for observations at high frequencies, these results demonstrate that the 100 m radio telescope can be successfully incorporated in global VLBI experiments at 3.5 mm wavelength.
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| 62. |
- Stannard, D., et al.
(författare)
-
VLBI Observations of 3C345 at 1.67 GHz
- 1980
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Ingår i: Monthly notices of the Royal Astronomical Society. - Oxford : Oxford University Press. - 0035-8711 .- 1365-2966. ; 192:4, s. 555-560
-
Tidskriftsartikel (refereegranskat)abstract
- VLBI observations of the quasar 3C 345 suggest that the milliarcsec subcomponents in the core have approximately equal intensities at 1.67 GHz. A new compact feature is detected in the inner jet structure at a distance of ∼ 12 m.arcsec from the core. © 1980 Royal Astronomical Society. Provided by the NASA Astrophysics Data System
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| 63. |
- Tang, G., et al.
(författare)
-
Radio source structure from geodetic VLBI observations : evolution of the quasar 3C 345 at 8 GHz
- 1989
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Ingår i: Astronomy and Astrophysics. - Les Ulis : EDP Sciences. - 0004-6361 .- 1432-0746. ; 216:1-2, s. 31-38
-
Tidskriftsartikel (refereegranskat)abstract
- Eight VLBI maps of 3C 345 were obtained at 8.3 GHz between 1980 and 1986. During this period, the two jet components C4 and C5 were shown to emerge from the core in succession and to move superluminally toward the west with angular velocities of 0.17 + or - 0.5 and 0.11 + or - 0.02 mas/yr, respectively. An emission detected between D and C5 after 1985.46 suggests that a new component emerged from the core, moving at an angular velocity of 0.2 mas/yr. The C3 component retained a velocity of about 0.44 mas/yr, and its proper motion was found to accelerate in the y-direction and decelerate in the x-direction.
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| 64. |
- Tang, Guoquiang, et al.
(författare)
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Radio source structure from geodetic VLBI observations : 8 GHz multi-epoch maps of the quasar 4C 39.25
- 1987
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Ingår i: Astronomy and Astrophysics. - Les Ulis : EDP Sciences. - 0004-6361 .- 1432-0746. ; 185:1-2, s. 87-93
-
Tidskriftsartikel (refereegranskat)abstract
- Techniques for estimating and/or eliminating the effects of structure variations in the extragalactic radio sources used as fiducial points in 8.3-GHz geodetic VLBI observations are described and demonstrated. Particular attention is given to the data base statistics, the calibration of visibility data, the production of hybrid maps with AIPS, and the implementation of these steps in a software package. A set of X-band maps of 4C 39.25, obtained with the receivers of the Mark III dual-frequency VLBI network at six epochs during 1980-1985, is presented. Such maps are shown to be of value (1) for maintaining submarcsec accuracy in the extragalactic reference frame and (2) for qualitative astronomical monitoring of the sources. In 4C 39.25, for example, apparent superluminal motions, complex internal kinematics, and a double western component are observed.
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| 65. |
- Tang, G., et al.
(författare)
-
Recent Evolution of Jet Components in 3C345 at 3.6 cm
- 1990
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Ingår i: Parsec-Scale radio jets. - Cambridge : Cambridge University Press. - 0521392268 ; , s. 32-37
-
Bokkapitel (refereegranskat)abstract
- A series of 3.6 cm VLBI maps of 3C345 (1980.79 to 1988.38) is presented. The evolution of the jet components in this quasar is briefly discussed. Recent behavior of component C5 is described and the presence of a new component, tentatively labeled C6, is suggested.
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| 66. |
- Zensus, J. A., et al.
(författare)
-
The inner radio jet of 3C273
- 1988
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Ingår i: Nature. - London : Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 334:6181, s. 410-412
-
Tidskriftsartikel (refereegranskat)abstract
- Radio maps of 3C273 obtained with very long baseline interferometry (VLBI) have been limited by low dynamic range and poor north-south resolution resulting from the low declination (2°) of this quasar1. Dramatic improvement can now be achieved using larger arrays and antennas in the Southern Hemisphere2,3. A new VLBI map, made at 5 GHz with angular resolution and dynamic range unsurpassed at this frequency for this source, shows a narrow jet extending to a projected distance lproj∼125 h-;1 parsecs from the core. Superluminal motion exists out to at least lproj≈46h-1 parsecs. Successive superluminal components emerge from the core and appear to move on a fixed curved path with similar speeds of about 1 milliarcseconds per year. © 1988 Nature Publishing Group.
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| 67. |
- Zhang, F. J., et al.
(författare)
-
1404+286 : A non-ideal calibrator for VLBI observations
- 1994
-
Ingår i: Astronomy and Astrophysics. - Les Ulis : EDP Sciences. - 0004-6361 .- 1432-0746. ; 281:3, s. 649-652
-
Tidskriftsartikel (refereegranskat)abstract
- The radio source 1404+286 was observed with global VLBI arrays at 5 and 1.67 GHz in 1990.88 and 1991.45 respectively. High quality maps are presented in this paper, and show the source to be resolved at both frequencies with a core-jet like structure extending approximately 6 mas in position angle approximately -145-degrees. The jet direction is similar in both maps. 1404+286 has often been used in the past as a flux density calibrator or a phase referencing source. Our results show that this source is not an ideal calibrator on VLBI scales.
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| 68. |
- Zhang, F.J., et al.
(författare)
-
Are there two engines at the center of 3C 286?
- 1994
-
Ingår i: Astronomy and Astrophysics. - Les Ulis : EDP Sciences. - 0004-6361 .- 1432-0746. ; 287:1, s. 32-37
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents images of the compact steep-spectrum quasar 3C 286 obtained with global VLBI arrays at 4.99 and 1.66 GHz. The morphology appears to be intermediate between the core-jet types and grossly distorted objects. The central portion is resolved into two components of almost equal peak brightnesses and spectral indices. On the 1.66 GHz map, the jet extends in position angle approximately -136-degrees, up to a knot (W1) (approximately 75 mas from the component C2) from which it curves rapidly towards the west to form another knot (W2). It is possible that the VLBI jet bends further towards the secondary component separated from the core by approximately 2.6'' in p.a. -115-degrees seen in high dynamic range VLA or Merlin maps. The jet has a sinuous feature shown clearly on the 5 GHz map. There is a low brightness extension at the North (designated N1) shown on both the 1.66 and 5 GHz maps, which is connected to the component C1 and bends towards the east.
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| 69. |
- Zhang, F.J., et al.
(författare)
-
The radio fine structure of the BL Lacertae object Mk 421
- 1990
-
Ingår i: Astronomy and Astrophysics. - Les Ulis : EDP Sciences. - 0004-6361 .- 1432-0746. ; 236:1, s. 47-52
-
Tidskriftsartikel (refereegranskat)abstract
- The BL Lac object Markarian 421 (Mk 421) has been mapped using VLBI arrays at a wavelength of 6 cm on four epochs from 1980.41 to 1983.43. It has a core-jet like structure with the jet pointing to the direction of NW with a stable position angle of about -45 deg. Almost all of the flux variation is accounted for by the change of the peak flux density of a compact component in the core. The results show that Mk 421 may exhibit apparent superluminal motion with apparent transverse speeds of components of (1.92 + or - 0.03)c (from 1981.25 to 1981.94) and (1.79 + or - 0.23)c (from 1981.94 to 1983.43) for C1; and (1.36 + or - 0.22)c for C2. The position angles of both the components C1 and C2 are nearly the same as the position angle of the jet, and there is no significant change of position angle as they move away from the core.
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| 70. |
- Zhang, F. J., et al.
(författare)
-
THE SUBMILLIARCSECOND RADIO STRUCTURES OF THE 2 BL LAC OBJECTS MKN421 AND 0735 + 178
- 1991
-
Ingår i: Monthly notices of the Royal Astronomical Society. - Oxford : Oxford University Press. - 0035-8711 .- 1365-2966. ; 248:3, s. 566-571
-
Tidskriftsartikel (refereegranskat)abstract
- Very high-resolution (approximately 0.15 mas) VLBI hybrid maps of the two BL Lac objects Mkn421 and 0735 + 178 have been produced at lambda-1.35 cm. The structures of both sources are simple. Only an unresolved core is found in Mkn421. It is magnetic field dominated, and the motion of relativistic electrons is strongly restrained by the magnetic field. Relativistic electrons with relatively low energy are responsible for the synchrotron radiation. The maps of 0735 + 178 show that the radio structure at lambda-1.35 cm is dominated by a strong core, and there is a weak component outside. We can put a lower limit to the angular velocity of the outer component (0.32 +/- 0.03) mas yr-1, corresponding to an apparent transverse speed of (5.4 +/- 0.6)c which tallies with previous results. The outer component has an extension towards the south-east, a tendency also seen in the 6-cm VLBI maps. With our 1.35-cm VLBI observations, we demonstrate that it is possible to study a new component emerging from its core during an outburst and to study its behaviour on its way out.
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