| 1. |
- Bååth, L.B. 1948-, et al.
(author)
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The microarcsecond structure of 3C 273 at 3 MM
- 1991
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In: Astronomy and Astrophysics. - Les Ulis : EDP Sciences. - 0004-6361 .- 1432-0746. ; 241:1, s. L1-L4
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Journal article (peer-reviewed)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.
(author)
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VLBI observations of active galactic nuclei at 3 MM
- 1992
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In: Astronomy and Astrophysics. - Les Ulis : EDP Sciences. - 0004-6361 .- 1432-0746. ; 257:1, s. 31-46
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Journal article (peer-reviewed)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.
(author)
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A 100 GHZ map of 3C 446
- 1993
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In: Astronomy and Astrophysics. - Les Ulis : EDP Sciences. - 0004-6361 .- 1432-0746. ; 280:1, s. 117-120
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Journal article (peer-reviewed)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. |
- Marcaide, J. M., et al.
(author)
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Discovery of shell-like radio-structure in SN1993J
- 1995
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In: Nature. - London : Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 373:6509, s. 44-45
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Journal article (peer-reviewed)abstract
- SUPERNOVA explosions are poorly understood, partly because of difficulties in modelling them theoretically(1), and partly because there have been no supernovae observed in our Galaxy since the invention of the telescope. But the recent discovery(2) of supernova SN1993J in the nearby galaxy M81 offers an opportunity to investigate the evolution of the remnant, and its interaction with the surrounding interstellar medium, at high resolution. Here we present radio observations of SN1993J, made using very-long-baseline interferometry, which show the development of a shell structure. This 8-month-old radio shell is the youngest ever discovered in a supernova. The data suggest that the supernova explosion and the expanding shell of the remnant have nearly spherical symmetry, with small deviations where some parts of the shell are brighter than others. If these deviations arise because of variations in the density of the shell, this may reconcile earlier reports of symmetric radio emission(3) with the observed optical asymmetry(4,5), as the density variations could easily cause the latter. We infer that the radio emission is generated at the interface(6-9), where the surrounding gas is shocked by the ejecta.
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| 5. |
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| 6. |
- Rantakyrö, F.T., et al.
(author)
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50 μas resolution VLBI images of AGN’s at λ3 mm
- 1998
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In: Astronomy and Astrophysics. - Berlin : Springer-Verlag. - 0004-6361 .- 1432-0746. ; 131, s. 451-467
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Journal article (peer-reviewed)abstract
- We present 15 images from the global mm-VLBI sessions in 1990 April at 100 GHz and 1993 April at 86 GHz. These observations probe the central engines of the 16 observed AGN's with up to 50 mu as resolution. Among other sources previously observed with lambda 3 mm VLBI we present the first lambda 3 mm maps of 0735+178, 0748+126, 1055+018, 2145+067, and CTA102, in total we have been able to image 13 out of the 16 observed sources. 6 out of the 13 imaged sources observed exhibit curvature and rapid structural changes, although the low dynamic range in two thirds of the maps limits the detection of weak features. Most of the sources have unresolved cores even at this high resolution. There is substantial evidence that the observed sources can be grouped into two general groups: A misaligned population with parsec scale jets in the form of low pitch helices and an aligned population with straight jets with small changes in PA due to intrinsic bends.
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