Astronomy and Astrophysics

Astronomy and Astrophysics

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 ben...

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Hauptverfasser: Krichbaum T.P. , Max Planck Institut für Radioastronomie, Bonn, Germany, Alberdi A. , Laboratorio de Astrofísica Espacial y Física Fundamental, Madrid, Spain, Instituto de Astrofísica de Andalucía CSIC, Granada, Spain, 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, Alberdi A., Laboratorio de Astrofísica Espacial y Física Alber, Madrid, Spain, Graham D.A., Max Planck Institut für Radioastronomie, Bonn, Germany, Count 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, Båth Lars B., Onsala Space Observatory, Colomer F., Onsala Space Observatory, 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, Standke K., Max Planck Institut für Radioastronomie, Bonn, Germany
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Zusammenfassung: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. Published 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_, lo