Volume 433, Number 3, April III 2005
|Page(s)||897 - 909|
|Published online||29 March 2005|
VLBI observations of weak sources using fast frequency switching
Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany e-mail: email@example.com;firstname.lastname@example.org
2 Geodätisches Institut der Universität Bonn, Nussallee 17, 53115 Bonn, Germany
3 National Radio Astronomy Observatory, PO Box 0, Socorro, NM, 87801, USA e-mail: email@example.com
4 ASTRON, PO Box 2, 7990 AA Dwingeloo, The Netherlands e-mail: firstname.lastname@example.org
Accepted: 17 December 2004
We have developed a new phase referencing technique for high frequency VLBI observations. In conventional phase referencing, one interleaves short scans on a nearby phase calibrator between the target source observations. In fast frequency switching described here, one observes the target source continuously while switching rapidly between the target frequency and a lower reference frequency. We demonstrate that the technique allows phase calibration almost reaching the thermal noise limit and present the first detection of the AGN in the FR I radio galaxy NGC 4261 at 86 GHz. Although point-like, this is the weakest source ever detected with VLBI at this frequency.
Key words: techniques: interferometric / techniques: high angular resolution / methods: observational / galaxies: active / galaxies: jets / galaxies: individual: NGC 4261
© ESO, 2005
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