| 1. |
- Bååth, L.B. 1948-, et al.
(författare)
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The microarcsecond structure of 3C 273 at 3 MM
- 1991
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Ingår i: Astronomy and Astrophysics. - Les Ulis : EDP Sciences. - 0004-6361 .- 1432-0746. ; 241:1, s. L1-L4
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Tidskriftsartikel (refereegranskat)abstract
- Recent improvements in data analysis and receiver techniques have allowed us to produce a map of the 100GHz emission from the compact radio source 3C273 with the unsurpassed resolution of 50-mu-as (microarcseconds). Our map shows that the structure within 300-mu-as (approximately 1.5.10(18).h-1 cm) has a position angle significantly different from the position angle of the jet observed at lower frequencies. There are also indications in our map that the inner structure has a more pronounced wiggling structure than has been observed on larger scales. The observations were made about 60 days from the start of the outburst of 1988. Most of the flux from the outburst is concentrated in a component which is elongated approximately (56 x 5).10(16).h-1 cm perpendicular to the overall jet-axis. The distance between this component and the core is approximately 128-mu-as, which corresponds to the distance expected from an apparent velocity of approximately 800-mu-as year-1.
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| 2. |
- Bååth, L.B. 1948-, et al.
(författare)
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VLBI observations of active galactic nuclei at 3 MM
- 1992
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Ingår i: Astronomy and Astrophysics. - Les Ulis : EDP Sciences. - 0004-6361 .- 1432-0746. ; 257:1, s. 31-46
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Tidskriftsartikel (refereegranskat)abstract
- Recent improvements in data analysis and receiver techniques have allowed us to produce maps of the 100 GHz emission from the compact cores of active galactic nuclei with the unsurpassed resolution of 50-mu-as (microarcseconds). We present here hybrid maps of a set of compact radio sources observed at two epochs with a global VLBI array. The high resolution enables us to show details of active galactic nuclei on size scales of 10(16)-10(17) cm. Jets are shown to be more curved in these inner parts than further out in the areas mapped with VLBI at lower frequencies. Our maps of the quasar 3C345 show that the curvature seen with lower resolution instruments continues very close to the core. New components are seen separating from the cores of 3C84 and BL Lac. We observe a component in 3C84 separating from the core with an apparent speed approximately 21000 km sec-1. The radio source OJ287 is still unresolved with our array, having a core size of less-than-or-similar-to 10(17) cm. There is no indication of any compact component in 3C279 which would be associated with the outburst in integrated flux density which happened some months before our observation. The flux density of the most compact component we observe in 3C279 agrees well with that of the quiet core as extrapolated from its radio spectrum at lower frequencies. The inner part of the radio jet of the giant elliptical galaxy M87 also shows a continuation of the structure on a larger size scale, with a structure we interpret as parts of a helical pattern. No fringes were found for 4C39.25 or Sgr A.
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| 3. |
- Lerner, M.S., et al.
(författare)
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A 100 GHZ map of 3C 446
- 1993
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Ingår i: Astronomy and Astrophysics. - Les Ulis : EDP Sciences. - 0004-6361 .- 1432-0746. ; 280:1, s. 117-120
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Tidskriftsartikel (refereegranskat)abstract
- The first map made from 100 GHz VLBI observations of the quasar/BL Lac object 3C446 is presented. This map represents a 25-fold increase in resolution compared to earlier maps. Our main conclusions are that the core of 3C 446 is still almost unresolved (less than or similar to 30 muas) at this frequency and that a jet extends several hundred microarcseconds at position angle almost-equal-to -142-degrees. A comparison is also made with observations at other size scales.
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| 4. |
- Doeleman, S., et al.
(författare)
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86 GHz Global VLBI Progress Report
- 1993
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Ingår i: VLBI Technology. - Tokyo : Terrapub. - 4887041128 ; , s. 89-92
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Bokkapitel (refereegranskat)
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| 5. |
- 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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| 6. |
- Akujor, Chidi E., et al.
(författare)
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Combined-Array Imaging of Extra-Galactic Radio Sources
- 1994
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Ingår i: Astronomy with Millimeter and Submillimeter Wave Interferometry. - San Francisco : Astronomical Society of the Pacific. - 0937707783 ; , s. 123-124
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Konferensbidrag (refereegranskat)
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| 7. |
- Chu, H.S., et al.
(författare)
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AO 0235+164 - A "Heretic" BL Lac
- 1994
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Ingår i: VLBI TECHNOLOGY. - Tokyo : Terra Scientific Publishing Company. ; , s. 146-155
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Bokkapitel (refereegranskat)
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| 8. |
- Okopi, J. E., et al.
(författare)
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Wide field mapping of 5C12
- 1991
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Ingår i: Radio Interferometry. - San Francisco, USA : Astronomical Society of the Pacific. - 0937707384 - 9780937707388 ; , s. 253-256
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Konferensbidrag (refereegranskat)abstract
- A wide-field mapping technique aimed at resolving problems which occur in the radio mapping of very wide fields is described. The technique has been successfully applied to Merlin observations of the 5C12 region covering an area of 1800 arcsec x 180 arcsec.
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| 9. |
- Zhang, F. J., et al.
(författare)
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1404+286 : A non-ideal calibrator for VLBI observations
- 1994
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Ingår i: Astronomy and Astrophysics. - Les Ulis : EDP Sciences. - 0004-6361 .- 1432-0746. ; 281:3, s. 649-652
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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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| 10. |
- Zhang, F.J., et al.
(författare)
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Are there two engines at the center of 3C 286?
- 1994
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Ingår i: Astronomy and Astrophysics. - Les Ulis : EDP Sciences. - 0004-6361 .- 1432-0746. ; 287:1, s. 32-37
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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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