Astronomy and Astrophysics – Astrophysics
Scientific paper
2008-02-21
A&A 483 (2008), 759-768
Astronomy and Astrophysics
Astrophysics
11 pages, 8 figures, 2 tables, accepted for publication in the Astronomy and Astrophysics; minor corrections to the manuscript
Scientific paper
10.1051/0004-6361:20078679
The apparent position of the "core" in a parsec-scale radio jet (a compact, bright emitting region at the narrow end of the jet) depends on the observing frequency, owing to synchrotron self-absorption and external absorption. While providing a tool probing physical conditions in the vicinity of the core, this dependency poses problems for astrometric studies using compact radio sources. We investigated the frequency-dependent shift in the positions of the cores (core shift) observed with very long baseline interferometry (VLBI) in parsec-scale jets. We discuss related physics, as well as its effect on radio astrometry and the connection between radio and optical positions of astrometric reference objects. We searched for the core shift in a sample of 277 radio sources imaged at 2.3 GHz (13 cm) and 8.6 GHz (4 cm) frequency bands using VLBI observations made in 2002 and 2003. The core shift was measured by referencing the core position to optically thin jet features whose positions are not expected to change with frequency. We present here results for 29 selected active galactic nuclei (AGN) with bright distinct VLBI jet features that can be used in differential measurements and that allow robust measurements of the shift to be made. In these AGN, the magnitude of the measured core shift between 2.3 and 8.6 GHz reaches 1.4 mas, with a median value for the sample of 0.44 mas. Nuclear flares result in temporal variability of the shift. An average shift between the radio (4 cm) and optical (6000 Angstrom) bands is estimated to be approximately 0.1 mas, and it should be taken into account in order to provide the required accuracy of the radio-optical reference frame connection. This can be accomplished with multi-frequency VLBI measurements... (abridged)
Kovalev Yu. Yu.
Lobanov Andrei P.
Pushkarev Aleksandr B.
Zensus Anton J.
No associations
LandOfFree
Opacity in compact extragalactic radio sources and its effect on astrophysical and astrometric studies does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Opacity in compact extragalactic radio sources and its effect on astrophysical and astrometric studies, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Opacity in compact extragalactic radio sources and its effect on astrophysical and astrometric studies will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-578319