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  • 1.
    Alberdi, A.
    et al.
    Laboratorio de Astrofísica Espacial y Física Fundamental, Madrid, Spain; Instituto de Astrofísica de Andalucía CSIC, Granada, Spain.
    Krichbaum, T.P.
    Max Planck Institut für Radioastronomie, Bonn, Germany.
    Graham, D.A.
    Max Planck Institut für Radioastronomie, Bonn, Germany.
    Greve, A.
    IRAM, Domaine Universitaire, Grenoble, France.
    Grewing, M.
    IRAM, Domaine Universitaire, Grenoble, France.
    Marcaide, J.M.
    Departamento de Astronomía Universitat de Valéncia, Spain.
    Booth, R.S.
    Onsala Space Observatory.
    Bååth, Lars B.
    Onsala Space Observatory.
    Colomer, F.
    Onsala Space Observatory; Observatorio de Yebes, Guadalajara, Spain.
    Doeleman, S.
    NEROC, Haystack Observatory, Westford, Massachusetts, USA.
    Marscher, A.P.
    Boston University, Boston, MA, USA.
    Rogers, A.E.E.
    NEROC, Haystack Observatory, Westford, Massachusetts, USA.
    Schalinski, C.J.
    IRAM, Domaine Universitaire, Grenoble, France; Institut für Weltraumsensorik (DLR), Berlin, Germany.
    Standke, K.
    Max Planck Institut für Radioastronomie, Bonn, Germany.
    The high-frequency compact radio structure of the peculiar quasar 4C 39.251997In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 327, no 2, p. 513-521Article in journal (Refereed)
    Abstract [en]

    We present new high angular resolution images of the compact non-thermal radio source 4C 39.25 obtained from VLBI observations at λ1.3cm, λ7mm, and λ3mm wavelengths. These maps and Gaussian model-fits show that the milli-arcsecond to sub-milliarcsecond structure of 4C 39.25 consists of a complex bent core-jet structure with embedded moving and stationary VLBI components. Facilitated by the small observing beams and high angular resolutions obtained at mm-wavelengths, we measured the relative positions of the jet components with an accuracy of a few hundred micro-arcseconds. This allows the detailed followup of the ongoing merging process of a westward superluminally moving component (b_) with a stationary component a_, located at ~2.9 mas east of the putative core d_. In contrast to the other components of the structure with steeper spectra, the westernmost component d_ exhibits an inverted spectrum peaking between λ7mm and λ3mm, thus further supporting its identification as the VLBI core, self-absorbed at longer wavelengths. From two VLBI maps obtained nearly simultaneously at λ7mm and λ1.3cm, we made the first spectral index map of 4C 39.25 in this wavelength regime. The main characteristics of the spectral index distribution of the jet are pronounced changes of the spectral index between orientations parallel and transverse to the jet axis. Near the merging components a_ and b_ the spectral index steepens with increasing separation from d_. However, in the bridge of emission c_, which connects d_ with a_ and b_, the spectral index gradient has a direction transverse to the jet axis, suggesting a frequency dependent jet curvature and edge-brightening. A brief discussion of this behaviour within current jet models is presented.

  • 2.
    Bååth, L.B.
    et al.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Cotton, W. D.
    Massachusetts Institute of Technology, Cambridge, MA, USA.
    Counselman, C. C.
    Massachusetts Institute of Technology, Cambridge, MA, USA.
    Shapiro, I. I.
    Massachusetts Institute of Technology, Cambridge, MA, USA.
    Wittels, J. J.
    Massachusetts Institute of Technology, Cambridge, MA, USA.
    Hinteregger, H. F.
    Haystack Observatory, Westford, MA, USA.
    Knight, C. A.
    Haystack Observatory, Westford, MA, USA.
    Rogers, A. E. E.
    Haystack Observatory, Westford, MA, USA.
    Whitney, A. R.
    Haystack Observatory, Westford, MA, USA.
    Clark, T. A.
    Goddard Space Flight Center, Greenbelt, MD, USA.
    Hutton, L. K.
    Goddard Space Flight Center, Greenbelt, MD, USA.
    Niell, A. E.
    Jet Propulsion Laboratory, Pasadena, CA, USA.
    Time-Dependent Radio Fine Structure of the Compact Sources NRAO 150 and 4C 39.251980In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 86, no 3, p. 364-372Article in journal (Refereed)
    Abstract [en]

    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.

  • 3.
    Bååth, L.B.
    et al.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Elgered, G.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Lundqvist, G.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Graham, D.
    Max-Planck-Institut für Radioastronomie, Bonn, Germany.
    Weiler, K. W
    Max-Planck-Institut für Radioastronomie, Bonn, Germany.
    Seielstad, G. A.
    Owens Valley Radio Observatory, Big Pine, CA, USA.
    Tallqvist, S.
    Helsinki University of Technology, Radio Laboratory, Espoo, Finland.
    Schilizzi, R. T.
    Netherlands Foundation for Radio Astronomy, Dwingenloo, The Netherlands.
    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 GHz1981In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 96, no 1-2, p. 316-324Article in journal (Refereed)
    Abstract [en]

    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°.

  • 4.
    Bååth, L.B.
    et al.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Padin, S.
    Owens Valley Observatory, Pasadena, CA, USA.
    Woody, D.
    Owens Valley Observatory, Pasadena, CA, USA.
    Rogers, A. E. E.
    Northeast Radio Observatory Corp., Haystack Observatory, Westford, MA, USA.
    Wright, M. C. H.
    University of California, Berkeley, CA, USA.
    Zensus, A.
    Owens Valley Observatory, Pasadena, CA, USA.
    Kus, A. J.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Backer, D. C.
    University of California, Berkeley, CA, USA.
    Booth, R. S.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Carlstrom, J. E.
    University of California, Berkeley, CA, USA.
    Dickman, R. L.
    UIniversity of Massachusetts, Amherst, MA, USA.
    Emerson, D. T.
    NRAO, Tucson, AZ, USA.
    Hirabayashi, H.
    Nobeyama Radio Observatory, Minamimaki, Nagano, Japan.
    Hodges, M. W.
    Owens Valley Observatory, Pasadena, CA, USA.
    Inoue, M.
    Nobeyama Radio Observatory, Minamimaki, Nagano, Japan.
    Moran, J. M.
    Center for Astrophysics, Cambridge, MA, USA.
    Morimoto, M.
    Nobeyama Radio Observatory, Minamimaki, Nagano, Japan.
    Payne, J.
    NRAO, Tucson, AZ, USA.
    Plambeck, R. L.
    University of California, Berkeley, CA, USA.
    Predmore, C. R.
    UIniversity of Massachusetts, Amherst, MA, USA.
    Rönnäng, B.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    The microarcsecond structure of 3C 273 at 3 MM1991In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 241, no 1, p. L1-L4Article in journal (Refereed)
    Abstract [en]

    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.

  • 5.
    Bååth, L.B.
    et al.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Rogers, A.E.E.
    Haystack Observatory, Westford, MA, USA.
    Inoue, M.
    Nobeyama Radio Observatory, Nobeyama, Minamisaku, Nagano, Japan.
    Padin, S.
    Owens Valley Observatory, Pasadena, CA, USA.
    Wright, M.C.H.
    University of California, Berkeley, CA, USA.
    Zensus, A.
    National Radio Astronomy Observatory, Socorro, NM, USA.
    Kus, A.J.
    Torun Radio Observatory, Torun, Poland.
    Backer, D.C.
    University of California, Berkeley, CA, USA.
    Booth, R.S.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Carlstrom, J.E.
    University of California, Berkeley, CA, USA.
    Dickman, R.L.
    University of Massachusetts, AMherst, MA, USA.
    Emerson, D.T.
    National Radio Astronomy Observatory, Tucson, AZ, USA.
    Hirabayashi, H.
    Nobeyama Radio Observatory, Nobeyama, Minamisaku, Nagano, Japan.
    Hodges, M.W.
    Owens Valley Observatory, Pasadena, CA, USA.
    Kobayashi, H.
    Nobeyama Radio Observatory, Nobeyama, Minamisaku, Nagano, Japan.
    Lamb, J.
    National Radio Astronomy Observatory, Tucson, AZ, USA.
    Moran, J.M.
    Center for Astrophysics, Cambridge, MA, USA.
    Morimoto, M.
    Nobeyama Radio Observatory, Nobeyama, Minamisaku, Nagano, Japan.
    Plambeck, R.L.
    University of California, Berkeley, CA, USA.
    Predmore, C.R.
    University of Massachusetts, AMherst, MA, USA.
    Rönnäng, B.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Woody, D.
    Owens Valley Observatory, Pasadena, CA, USA.
    VLBI observations of active galactic nuclei at 3 MM1992In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 257, no 1, p. 31-46Article in journal (Refereed)
    Abstract [en]

    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.

  • 6.
    Bååth, L.B.
    et al.
    Onsala Space Observatory, Onsala, Sweden.
    Zhang, F. J.
    Shanghai Observatory, China.
    IMAGES OF THE BL LACERTAE OBJECT 1749+701 AT 5 GHZ1992In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 262, no 1, p. 1-7Article in journal (Refereed)
    Abstract [en]

    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.

  • 7.
    Bååth, L.B.
    et al.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Zhang, F. J.
    Nuffield Radio Astronomy Laboratories, Jodrell Bank, Macclesfield, Cheshire, United Kingdom.
    Chu, H. S.
    Purple Mountain Observatory, Nanjing, China.
    0735+178: The cosmic conspiracy1991In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 250, no 1, p. 50-56Article in journal (Refereed)
    Abstract [en]

    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.

  • 8.
    Bååth, L.B.
    et al.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Zhang, F.J.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    The radio fine structure of the BL Lacertae object 0735 + 1781991In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 243, no 2, p. 328-332Article in journal (Refereed)
    Abstract [en]

    The BL Lacertae object 0735 + 178 has been mapped with global VLBI arrays at four epochs from 1979 to 1983. The hybrid maps presented in this paper show a complex structure with a component separating from the core with an apparent transverse velocity of almost-equal-to 7.9 c. We suggest a model in which new components are born in the core during an outburst, initially move away towards northeast and then at a distance of almost-equal-to 4.2 mas turn towards the southeast. At this point, the component does not show any discernible motion away from the core. We suggest that the jet curls towards the south and towards the observer and at this point has its minimum viewing angle, with maximum boosting and minimum apparent velocity. We associate the outburst of 1989 with the event when a superluminally moving component reaches this point.

  • 9. Chu, H.S.
    et al.
    Bååth, Lars B.
    Halmstad University, School of Business and Engineering (SET).
    Rantakyrö, F.T.
    Halmstad University, School of Business and Engineering (SET).
    Zhang, F.J.
    Nicholson, G.
    VLBI observations of the puzzling BL Lacertae object 0235+1641996In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 307, no 1, p. 15-20Article in journal (Refereed)
    Abstract [en]

    For over 20 years, many models have been proposed to explain the variability of AO0235+164. Among them, the most favorable has been micro-lensing. We have made a series of VLBI observations on this source in order to better understand its nature. The resultant maps indicate dramatic changes in the position angle of the jet between observations as well as a correlation between the intensity of the VLBI core and flux outbursts which occurred between the observing sessions. These characteristics, in conjunction with other arguments, suggest that the source variability is intrinsic, i.e. microlensing is of minor importance. We suggest two models: 1) a model in which the jet starts at a very small angle to the line of sight and then curves away to become about 6deg at about 1 mas from the core; and 2) a CME (Coronal Mass Ejection) model that also may explain the violent variability in intensity, polarization position angle, and jet direction in AO0235+164.

  • 10.
    Lerner, M.S.
    et al.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Bååth, L.B.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Inoue, M.
    Nobeyama Radio Observatory, Minamimaki, Nagano, Japan.
    Padin, S.
    Owens Valley Radio Observatory, California Institute of Technology, Pasadena, CA, USA.
    Rogers, A.E.E.
    Northeast Radio Observatory Corp., Haystack Observatory, Westford, MA, USA.
    Wright, M.C.H.
    University of California, Berkeley, CA, USA.
    Zensus, A.
    NRAO, Soccoro, NM, USA.
    Backer, D.C.
    University of California, Berkeley, CA, USA.
    Booth, R.S.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Carlstrom, J.E.
    Owens Valley Radio Observatory, California Institute of Technology, Pasadena, CA, USA.
    Emerson, D.T.
    NRAO, Tucson, AZ, USA.
    Hirabayashi, H.
    Nobeyama Radio Observatory, Minamimaki, Nagano, Japan.
    Hodges, M.W.
    Owens Valley Radio Observatory, California Institute of Technology, Pasadena, CA, USA.
    Jewell, P.
    NRAO, Soccoro, NM, USA.
    Kobayashi, H.
    Nobeyama Radio Observatory, Minamimaki, Nagano, Japan.
    Kus, A.J.
    Torun Radio Observatory, Nicolaus Copernicus University, Torun, Poland.
    Moran, J.M.
    Center for Astrophysics, Cambridge, MA, USA.
    Morimoto, M.
    Nobeyama Radio Observatory, Minamimaki, Nagano, Japan.
    Plambeck, R.L.
    University of California, Berkeley, CA, USA.
    Rantakyrö, F.T.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Woody, D.
    Owens Valley Radio Observatory, California Institute of Technology, Pasadena, CA, USA.
    A 100 GHZ map of 3C 4461993In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 280, no 1, p. 117-120Article in journal (Refereed)
    Abstract [en]

    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.

  • 11.
    Marcaide, J. M.
    et al.
    Massachusetts Institute of Technology, Cambridge, MA, USA & Max-Planck-Institut für Radioastronomie, Bonn, Germany.
    Shapiro, I. I.
    Massachusetts Institute of Technology, Cambridge, MA, USA & Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA.
    Corey, B. E.
    Massachusetts Institute of Technology, Cambridge, MA, USA & Haystack Observatory/NEROC, Westford, MA, USA.
    Cotton, W. D.
    National Radio Astronomy Observatory, Charlottesville, VA, United States.
    Gorenstein, M. V.
    Massachusetts Institute of Technology, Cambridge, MA, USA & Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA.
    Rogers, A. E. E.
    Haystack Observatory/NEROC, Westford, MA, USA.
    Romney, J. D.
    Max-Planck-Institut für Radioastronomie, Bonn, Germany.
    Schild, R. E.
    Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA.
    Bååth, L.B.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Bartel, N.
    Massachusetts Institute of Technology, Cambridge, MA, USA & Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA.
    Cohen, N. L.
    Massachusetts Institute of Technology, Cambridge, MA, USA; Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA & Cornell University, Ithaca, NY, USA.
    Clark, T. A.
    NASA, Goddard Space Flight Center, Greenbelt, MD, USA.
    Preston, R. A.
    Jet Propulsion Laboratory, Pasadena, CA, USA.
    Ratner, M. I.
    Massachusetts Institute of Technology, Cambridge, MA, USA & Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA.
    Whitney, A. R.
    Haystack Observatory/NEROC, Westford, MA, USA.
    The quasars 1038+528 A and B1985In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 142, no 1, p. 71-84Article in journal (Refereed)
    Abstract [en]

    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.

  • 12. Matveenko, L.I.
    et al.
    Pauliny-Toth, L.I.K.
    Bååth, Lars B.
    Halmstad University, School of Business and Engineering (SET).
    Graham, D.A.
    Sherwood, W.A.
    Kus, A.J.
    The structure of the quasar 3C345 at lambda 49cm and its relation to low-frequency variability1996In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 312, p. 738-744Article in journal (Refereed)
    Abstract [en]

    The structure of the quasar 3C345 has been studied at lambda 49cm with a global VLBI network. The core has a low-freuqncy cut off in its spectrum, and is very weak at this wavelength. The most compact bright knot is the part of the jet nearest to the nucleus, with a size of about 5x4 mas and a brightness temperature of Tb about 0.6 10^12 K. Its flux density and solid angle increased by a factor of about 2 during the period 1983.9 to 1990.8, but the birghtness temperature did not change significantly. The emission at millimeter wavelengths decreased by a factor of about 2 during the same period, while the UV emission from the nucleus also dcreased. We suggest that variations in the low-frequency emissions are caused by changes in the absorption by a cocoon - the thermal plasma surrounding the jet. The electron density in the region is Ne about 10^5 cm^-3and the longitudal field is about 40 microG. The emission measure and the rotation measure vary with r, the distance from the nucleus as r^-3. The data at lamda 49cm indi´cate several components in and near the "hotspot" at the end of the arcsec jet.

  • 13.
    Rantakyrö, F. T.
    et al.
    University of Gothenburg, Gothenburg, Sweden.
    Bååth, L.B.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Pauliny-Toth, I. I. K.
    Max-Planck-Institut für Radioastronomie, Bonn, Germany.
    Matveyenko, L. I.
    Space Research Institute, Moscow, Russia.
    Unwin, S. C.
    California Institute of Technology, Pasadena, California, United States.
    High dynamic-range VLBI observations of 3C 345 at 18 cm wavelength1992In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 259, no 1, p. 8-16Article in journal (Refereed)
    Abstract [en]

    This paper presents very high dynamic range VLBI observations of the quasar 3C345 at 18 cm wavelength at two epochs, 1981.11 and 1985.27. We find that the direction of the jet changes drastically and the surface brightness decreases with increasing distance from the core. We show that a true three-dimensional curvature of the jet in space is needed to obtain the observed decrease of intensity with distance from the core, both in an adiabatic expansion model as well as in a model where the comoving flux is constant. Our observations confirm the detection of a previously reported low surface brightness component, C0. In addition, there is a large component extended perpendicular to the jet axis which we associate with a stationary shock at a distance consistent with the expected position of the narrow line region. Models for the intensity of the jet fitted to the observed dependence of intensity with distance from the core suggests this shocked region to be the place where the jet is expanding adiabatically after having had a constant width closer to the core. A limit on the allowed viewing angle theta less-than-or-similar-to 40-degrees is derived from the lack of any detectable counterjet.

  • 14.
    Rantakyrö, Fredrik T.
    et al.
    Dept. of Astronomy and Astrophysics, University of Gothenburg, S-412 96 Gothenburg, Sweden.
    Bååth, Lars B.
    Onsala Space Observatory, S-439 92 Onsala, Sweden.
    Dallacasa, Daniele
    Istituto di RadioAstronomia, CNR, Via Gobetti 101, I-40129, Bologna, Italy.
    Jones, Dayton L.
    Jet Propulsion Laboratory, Pasadena, CA 91109, United States.
    Wehrle, Ann E.
    Infrared Proc. and Analysis Center, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91125, United States.
    Multiband VLBI observations of CTA 1021996In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 310, no 1, p. 66-74Article in journal (Refereed)
    Abstract [en]

    The source CTA102, known to exhibit low frequency variability, has been observed at six epochs (three at λ32cm, two at λ18cm, and one at λ1.3cm) with intercontinental VLBI arrays. On the basis of the changes observed in the structure, we believe that the flux density variations at these wavelengths are due to intrinsic processes and not due to interstellar scintillation. This source exhibits behaviour suggestive of being expanding with a very high apparent transverse velocity.

  • 15.
    Rantakyrö, F.T.
    et al.
    Istituto di RadioAstronomia–CNR, Via Gobetti 101, I-40129, Bologna, Italy; Joint Institute for VLBI in Europe, Postbus 2, 7990AA Dwingeloo, The Netherlands .
    Bååth, Lars B.
    Halmstad University, School of Business and Engineering (SET).
    Backer, D.C.
    University of California, Berkeley CA 94720, U.S.A..
    Booth, R.S.
    Onsala Space Observatory, S-439 92 Onsala, Sweden.
    Carlström, J.E.
    Owens Valley Observatory, California Institute of Technology, Pasadena CA 91125, U.S.A..
    Emerson, D.T.
    NRAO, 949 N. Cherry Ave., Campus Bldg. 65, Tucson AZ 85721-0655, U.S.A..
    Grewing, M.
    IRAM, 300 rue de la Piscine, F-38406 St. Martin d’H`eres, France.
    Hirabayashi, H.
    Nobeyama Radio Observatory, Nobeyama, Minamisaku, Nagano 384-13, Japan.
    Hodges, M.W.
    Owens Valley Observatory, California Institute of Technology, Pasadena CA 91125, U.S.A..
    Inoue, M.
    Nobeyama Radio Observatory, Nobeyama, Minamisaku, Nagano 384-13, Japan.
    Kobayashi, H.
    Nobeyama Radio Observatory, Nobeyama, Minamisaku, Nagano 384-13, Japan.
    Krichbaum, T. P.
    Max-Planck-Institut fu ̈r Radioastronomie, Auf dem Huegel 69, D-53121 Bonn, Germany.
    Kus, A.J.
    Torun Radio Observatory, Nicolau Copernicus Observatory, Torun, Poland.
    Moran, J.M.
    Center for Astrophysics, 60 Garden Street, Cambridge MA 02138, U.S.A..
    Morimoto, M.
    Nobeyama Radio Observatory, Nobeyama, Minamisaku, Nagano 384-13, Japan.
    Padin, S.
    Owens Valley Observatory, California Institute of Technology, Pasadena CA 91125, U.S.A..
    Plambeck, R.L.
    University of California, Berkeley CA 94720, U.S.A..
    Predmore, R.
    FCRAO, Dept. of Physics and Astronomy, 619 Lederle Graduate Research Center, Univ. of Mass., Box 34517, Amherst, MA, U.S.A..
    Rogers, A.E.E.
    Northeast Radio Observatory Corp., Haystack Observatory, Westford MA 01886, U.S.A..
    Schalinski, C.
    IRAM, 300 rue de la Piscine, F-38406 St. Martin d’H`eres, France.
    Witzel, A.
    Max-Planck-Institut fu ̈r Radioastronomie, Auf dem Huegel 69, D-53121 Bonn, Germany.
    Woody, D.
    Owens Valley Observatory, California Institute of Technology, Pasadena CA 91125, U.S.A..
    Wright, M.C.H.
    University of California, Berkeley CA 94720, U.S.A..
    Zensus, A.
    NRAO, Socorro NM 87801, U.S.A..
    50 μas resolution VLBI images of AGN’s at λ3 mm1998In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 131, p. 451-467Article in journal (Refereed)
    Abstract [sv]

    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.

  • 16.
    Rantakyrö, F.T.
    et al.
    European Southern Observatory, Casilla 19001, Santiago 19, Chile; Observatorio Cerro Calan, Universidad de Chile, Santiago, Chile.
    Wiik, K.
    Tuorla Observatory, Väisäläntie 20, 21500 Piikkiö, Finland.
    Tornikoski, M.
    Metsähovi Radio Observatory, Metsähovintie 114, 02540 Kylmälä, Finland.
    Valtaoja, E.
    Tuorla Observatory, Väisäläntie 20, 21500 Piikkiö, Finland; Department of Physical Sciences, University of Turku, 20100 Turku, Finland.
    Bååth, Lars B.
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE).
    Multifrequency interferometer and radio continuum monitoring observations of CTA 1022003In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 42, no 5, p. 473-485Article in journal (Refereed)
    Abstract [en]

    This paper represents the work of several years of observation of CTA 102 with both single dish telescopes and

    interferometric arrays, covering wavelengths from 1.2 cm to 1.3 mm. The resolution of the maps covers an order of magnitude

    from 0.5 mas to 50 μas. The images presented demonstrate the rapid structural changes in this source. These rapid structural

    changes correlates with the outbursts seen in the total flux, turnover frequency and in the spectral index. We have calculated the

    Brightness Temperatures of the components (TB ) directly from the determined component sizes and also using the logarithmic

    variability amplitudes and timescales to calculate the TB s. Both the methods yielded measurements of source frame T Bs no

    higher than

    ∼a few × 10

    12

    K. We find that the observed average proper motion is

    0.4 0.07 mas/yr, which corresponds to an

    apparent transverse velocity of 11

    ± 2 c.

  • 17.
    Romney, J.
    et al.
    Max-Planck-Institut für Radioastronomie, Bonn, Germany.
    Padrielli, L.
    CNR, Istituto di Radioastronomia, Bologna, Italy.
    Bartel, N.
    Max-Planck-Institut für Radioastronomie, Bonn, Germany & Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA.
    Weiler, K.W.
    Max-Planck-Institut für Radioastronomie, Bonn, Germany & Division of Astronomical Sciences, National Science Foundation, Washington, DC, USA.
    Ficarra, A.
    CNR, Istituto di Radioastronomia, Bologna, Italy.
    Mantovani, F.
    CNR, Istituto di Radioastronomia, Bologna, Italy.
    Bååth, L.B.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Kogan, L.
    Institute for Space Research, Academy of Sciences, Moscow, USSR.
    Matveenko, L.
    Institute for Space Research, Academy of Sciences, Moscow, USSR.
    Moiseev, I.G.
    Crimea Astrophysical Observatory, Academy of Sciences, Moscow, USSR.
    Nicholson, G.
    National Institute for Telecommunications Research, Johannesburg, South Africa.
    The milliarcsecond scale structure of low frequency variable sources1984In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 135, no 2, p. 289-299Article in journal (Refereed)
    Abstract [en]

    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.

  • 18.
    Tang, G.
    et al.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Rönnäng, B.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Bååth, L.B.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Radio source structure from geodetic VLBI observations: evolution of the quasar 3C 345 at 8 GHz1989In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 216, no 1-2, p. 31-38Article in journal (Refereed)
    Abstract [en]

    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.

  • 19.
    Tang, Guoquiang
    et al.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Rönnäng, B.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Bååth, L.B.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Radio source structure from geodetic VLBI observations: 8 GHz multi-epoch maps of the quasar 4C 39.251987In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 185, no 1-2, p. 87-93Article in journal (Refereed)
    Abstract [en]

    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.

  • 20.
    Zhang, F. J.
    et al.
    Nuffield Radio Astronomy Laboratories, University of Manchester, Cheshire, UK.
    Bååth, L.B.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Spencer, R. E.
    Nuffield Radio Astronomy Laboratories, University of Manchester, Cheshire, UK.
    1404+286: A non-ideal calibrator for VLBI observations1994In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 281, no 3, p. 649-652Article in journal (Refereed)
    Abstract [en]

    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.

  • 21.
    Zhang, F.J.
    et al.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Bååth, L.B.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    The radio fine structure of the BL Lacertae object Mk 4211990In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 236, no 1, p. 47-52Article in journal (Refereed)
    Abstract [en]

    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.

  • 22.
    Zhang, F.J.
    et al.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Spencer, R.E.
    Nuffield Radio Astronomy Laboratories, Jodrell Bank, Macclesfield, Cheshire, United Kingdom.
    Schilizzi, R.T.
    Netherlands Foundation for Research in Astronomy, Dwingeloo, The Netherlands.
    Fanti, C.
    Dipartimento di Astronomia dell'Universita & Instituto di Radioastronomia CNR, Bologna, Italy.
    Bååth, L.B.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Su, B.M.
    Yunnan Observatory, Chinese Academy of Sciences, Kunming, China.
    Are there two engines at the center of 3C 286?1994In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 287, no 1, p. 32-37Article in journal (Refereed)
    Abstract [en]

    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.

1 - 22 of 22
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