| 1. |
- Bartel, N., et al.
(författare)
-
The Compact Radio Source 2021+614 : Simultaneous 2.3 and 8.3 GHz Mark III VLBI Observations
- 1984
-
Ingår i: Astrophysical Journal. - Philadelphia, PA : Institute of Physics Publishing (IOPP). - 0004-637X .- 1538-4357. ; 279:1, s. 116-121
-
Tidskriftsartikel (refereegranskat)abstract
- Second-epoch VLBI observations of the flat-spectrum radio source 2021+614 made simultaneously at 2.3 and 8.3 GHz with the Mark III system are reported. The maps derived from these observations reveal a complex, frequency-dependent radio structure on the milliarcsecond scale. The object has four nearly collinear components oriented at a position angle of about 35 degrees and embedded in an extended region. Two of these are optically thin, one has a flat spectrum, and the other appears to be synchrotron self-absorbed in the frequency range 2.3-8.3 GHz. No significant structural variation is found at either frequency between epochs separated by about three years. The formal estimate of the transverse velocity between two components, one with a flat and the other with an inverted spectrum, is v/c = 0.7 + or - 2.3. Remarkable similarities between 2021+614 and the unusual source 0316+413 are discussed.
|
|
| 2. |
- Booth, R. S., et al.
(författare)
-
High-resolution observations of quasars from the Parkes +/- 4 deg. sample
- 1979
-
Ingår i: Monthly notices of the Royal Astronomical Society. - Oxford : Oxford University Press. - 0035-8711 .- 1365-2966. ; 188, s. 159-163
-
Tidskriftsartikel (refereegranskat)abstract
- VLBI observations of 20 compact quasars have been made between Jodrell Bank and Onsala at a frequency of 1666 MHz. Twelve of the quasars have inverted or peaked spectra at centimetre wavelengths and these are all unresolved, having angular diameters of less than 0.015 arcsec. Two out of five quasars with overall flat spectra are partially resolved on this scale size, as are three steep-spectrum quasars.
|
|
| 3. |
- Borkowski, Kazimierz M., et al.
(författare)
-
Determination of the Toruń Antenna Position from VLBI Observations
- 1992
-
Ingår i: Acta Astronomica. - Warsaw : Fundacja Astronomii Polskiej im. Mikolaja Kopernika / Copernicus Foundation for Polish Astronomy. - 0001-5237. ; 42, s. 371-375
-
Tidskriftsartikel (refereegranskat)abstract
- Four strong radio sources were observed over a 12-hr session in March, 1990 between radio telescopes at Onsala and Torun at wavelength of 6 cm in the standard VLBI Mark II setup for the purpose of improving the coordinates of the Torun 15-meter antenna. The Cartesian coordinates of the antenna derived from the presented measurements are (in meters): 3638609.62 +/- 0.19, 1221773.23 +/- 0.54 and 5077024.50 +/- 1.66 in the x, y, and z directions, respectively.
|
|
| 4. |
- Bååth, L.B. 1948-, et al.
(författare)
-
0735+178 : The cosmic conspiracy
- 1991
-
Ingår i: Astronomy and Astrophysics. - Les Ulis : EDP Sciences. - 0004-6361 .- 1432-0746. ; 250:1, s. 50-56
-
Tidskriftsartikel (refereegranskat)abstract
- This paper discusses a radio outburst in the BL Lac-object 0735+178 which started in early 1988, ended during 1990 and was succeeded by a new outburst which is still in progress. Our image obtained with a global VLBI network shows the source to mainly consist of a core-jet like structure ending in diffuse emission region of low surface brightness located to the east of the core. We identify two new components as having been produced during the late 1980's. They are moving out with apparent superluminal motion in a viewing angle of greater-than-or-similar-to 10-degrees at a distance of less-than-or-similar-to 2 mas from the core. The core includes another new component, but our resolution is just sufficient to resolve out this component from the core at our epoch of observation. We suggest that the weak emission region is caused by an older component reaching the point at which the Doppler boosting is at its maximum and that the long time scale flux variation are due to successive events when evolved components reach that point.
|
|
| 5. |
- Bååth, L.B. 1948-
(författare)
-
A closer look at active galactic nuclei — the great engines of the universe
- 1992
-
Ingår i: Physica scripta. T. - Stockholm, Sweden : Kungliga Vetenskapsakademien. - 0281-1847. ; T43, s. 57-66
-
Tidskriftsartikel (refereegranskat)abstract
- The intensive radio emission from powerful radio galaxies and quasars Make these attractive candidates to become "standard candles" to probe the Universe. This paper discusses this possibility and the physics of the radio sources.
|
|
| 6. |
|
|
| 7. |
- Bååth, L.B. 1948-, et al.
(författare)
-
High Resolution Observations of the QSO 3C 345 at 1.3 centimeters
- 1981
-
Ingår i: Astrophysical Journal. - Philadelphia, PA : Institute of Physics Publishing (IOPP). - 0004-637X .- 1538-4357. ; 243, s. L123-L126
-
Tidskriftsartikel (refereegranskat)abstract
- High-resolution VLBI observations made at a frequency of 22.235 GHz of the quasar 3C 345 are discussed. Antennas located at the Crimean Astrophysical Observatory, USSR; Onsala, Sweden; Effelsberg, West Germany; and the Haystack Observatory, Massachusetts were employed at 4-min integration times to provide baselines ranging up to 5.5 x 10 to the 8th wavelengths. About 40% of the total flux density of 7.85 Jy, observed in November 1977, and 8.05 Jy, observed in October 1978, is found to originate in an unresolved component of the quasar core in a region less than 0.1 milliarcsec in diameter. The elongated jet-like component of the quasar is observed to contain several peaks of emission extending up to 6 milliarsec from the core which decreased in extent between the two observations.
|
|
| 8. |
- Bååth, L.B. 1948-, et al.
(författare)
-
IMAGES OF THE BL LACERTAE OBJECT 1749+701 AT 5 GHZ
- 1992
-
Ingår i: Astronomy and Astrophysics. - Les Ulis, France : EDP Sciences. - 0004-6361 .- 1432-0746. ; 262:1, s. 1-7
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents images of 1749+701 from data obtained between 1980 and 1983 as a part of our VLBI programme to monitor a subsample of BL Lac objects at 5GHz. Our images show that this source has a complex structure with a jet pointing towards the north-west at a position angle of about -65-degrees. The brightest component is growing in extension along this position angle. We suggest this to be the core and that the growing extension was caused by a shock generated during an outburst and moving out along the jet. From the extension rate, we obtain an angular separation speed of 0.18 mas yr-1, which corresponds to an apparent transverse speed of 5c. The distances and position angles of two outer components seem remarkably constant. The phenomenon can be understood through a model in which a relativistic jet bends such that its axis is very close to the line of sight in two points. We also deduce that the Lorentz factor must be 4.5 less-than-or-equal-to gamma less-than-or-equal-to 6.5 and that the viewing angle must be 5-degrees less-than-or-equal-to theta less-than-or-equal-to 10-degrees. In this paper, we also present two images obtained from 5GHz MERLIN and combined MERLIN-VLBI data respectively. These maps show that there is a weak component located at a distance of 0.42 arcsec from the core at p.a -155-degrees.
|
|
| 9. |
- Bååth, L.B. 1948-
(författare)
-
Radiospår i galaxhopar
- 1973
-
Ingår i: Astronomisk tidsskrift. - København/Oslo/Saltsjöbaden : Astronomisk Selskab/Norsk astronomisk selskap/Svenska astronomiska sällskapet. - 0004-6345. ; 6:1, s. 18-24
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
|
|
| 10. |
- Bååth, L.B. 1948-, et al.
(författare)
-
The microarcsecond structure of 3C 273 at 3 MM
- 1991
-
Ingår i: Astronomy and Astrophysics. - Les Ulis : EDP Sciences. - 0004-6361 .- 1432-0746. ; 241:1, s. L1-L4
-
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.
|
|
