| 1. |
- Bååth, L.B. 1948-, et al.
(författare)
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The Radio Fine Structure of the BL Lacertae Objects AO0235+164, 0735+178, BL Lac, 1749+701, Mk 421 and 3C 66 A at 5 GHz
- 1981
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Ingår i: Astronomy and Astrophysics. - Les Ulis : EDP Sciences. - 0004-6361 .- 1432-0746. ; 96:1-2, s. 316-324
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Tidskriftsartikel (refereegranskat)abstract
- Very long baseline interferometer observations at 4997 MHz (lambda = 6 cm) on European and intercontinental baselines with lengths up to 1.35 108lambda have been used to probe the milliarc s structure of the BL Lacertae objects AO 0235+164, 0735+178, BL Lac, 1749+701, Mk 421, and 3C 66A. Two sets of observations are reported, made in November 1978 and March 1979. AO 0235+164 and 0735+178 both showed structures consisting of a very bright, unresolved core and a jet-like component extending ˜5".4 10-3 along position angle ˜20° and ˜4".2 10-3 along position angle ˜45°, respectively. AO 0235+164 contained more than 98% of the total flux density within a diameter of ≲ 36" 10-3. BL Lac, 1749+701 and Mk 421 all showed evidence for a complex structure of several components, including an unresolved core. 3 C 66A was elongated along position angle ˜ -45°.
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| 2. |
- Bååth, L.B. 1948-, et al.
(författare)
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Time-Dependent Radio Fine Structure of the Compact Sources NRAO 150 and 4C 39.25
- 1980
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Ingår i: Astronomy and Astrophysics. - Les Ulis : EDP Sciences. - 0004-6361 .- 1432-0746. ; 86:3, s. 364-372
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Tidskriftsartikel (refereegranskat)abstract
- Very long baseline interferometer observations at 7.85 GHz have been used to probe the milliarcsecond structure of the unidentified, very compact radio source NRAO 150 and QSO 4 C 39.25. NRAO 150 exhibited no structural variations from 1972 to the end of 1974. A model with two circular Gaussian components fits the data well. NRAO 150 had a flux density of 7.6 plus or minus 0.5 Jy in the compact component; 4 C 39.25 showed a two-component structure, the components having a separation of (2.02 plus or minus 0.05 arc sec) x 10 to the -3rd power. The upper bound on the speed of transverse separation is 0.0001 arc sec per year or less than 2.7 c. From the spectrum there are also indications of a third, larger component.
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| 3. |
- Marcaide, J. M., et al.
(författare)
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The quasars 1038+528 A and B
- 1985
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Ingår i: Astronomy and Astrophysics. - Les Ulis : EDP Sciences. - 0004-6361 .- 1432-0746. ; 142:1, s. 71-84
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Tidskriftsartikel (refereegranskat)abstract
- The results of VLBI observations of the quasars 1038 + 528 A and B at 2.8, 3.6, 13, and 18 cm at various times between November 1979 and March 1981 are reported. The observations and data calibration are described, as are the mapping and astrometric techniques applied in the study. Both quasars are found to have 'core-jet' morphologies. The core of the A quasar dominates its morphology at centrimetric wavelengths with the brightness temperature of its 400 pc long jet being about 1/100 that of the core. By contrast, the 'jet' in the B quasar is very short (about 70 pc); the tail of this jet has the steepest spectral index found to date in extragalactic compact sources, indicating that high electron losses are responsible for the shortness of the jet. No evidence for appreciable morphological change in the B quasar was found over the time span of the study, whereas a new feature may be emerging from the A quasar core at superluminal speed.
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| 4. |
- Romney, J., et al.
(författare)
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The milliarcsecond scale structure of low frequency variable sources
- 1984
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Ingår i: Astronomy and Astrophysics. - Les Ulis : EDP Sciences. - 0004-6361 .- 1432-0746. ; 135:2, s. 289-299
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Tidskriftsartikel (refereegranskat)abstract
- VLBI observations were performed of 21 radio sources which exhibit low frequency variability. The integrated flux densities, variability indices at 0.4 GHz, optical magnitudes, redshifts, spectral indices at 0.4 GHz, and flux intensities with respect to a reference energy flux are provided. The VLBI data were synthesized from observatories located on different continents around the world. All structures were emitted from compact sources with sizes confined to milliarcsc scales. Nearly half displayed core-jet morphologies, while 28 percent had complex structures and 14 percent had either simple structures or were not resolvable. Further observations are proceeding at 400 mHz to confirm the presence of synchrotron electrons and magnetic fields ejected at relativistic speeds along the line of sight, which has the appearance of superluminal velocities.
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| 5. |
- Tang, G., et al.
(författare)
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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
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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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| 6. |
- 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
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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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