Publication Title

Proceedings of the 7th Symposium of the European VLBI Network on New Developments in VLBI Science and Technology

Publication Date

2004

Document Type

Conference Paper

First and Last Page

99

Abstract

We present current results from our ongoing project to study the parsec-scale relativistic jet kinematics of sources in the U.S. Naval Observatory's Radio Reference Frame Image Database (RRFID). The RRFID consists of snapshot observations using the VLBA plus up to 9 additional antennas at 8 and 2 GHz, and is intended to allow monitoring of these sources for variability or structural changes so they can be evaluated for continued suitability as radio reference frame objects. The Image Database currently contains about 3000 images of 450 sources from 1994 to 2004, with some sources having images at 20 epochs or more.

We have now completed analysis of the 8 GHz images for all sources observed at 3 or more epochs from 1994 to 1998. The completed analysis comprises 966 images of 87 sources, or an average of 11 epochs per source. Apparent jet speeds have been measured for these sources, and the resulting speed distribution has been compared with results obtained by other large VLBI surveys. The measured apparent speed distribution agrees with those found by the 2 cm survey and Caltech-Jodrell Bank (CJ) survey; however, when a source-by-source comparison is done with the 2 cm survey results, significant disagreement is found in the apparent speed measurements for a number of sources. This disagreement can be traced in most cases to either an insufficient time baseline for the current RRFID results, or to apparent component mis-identification in the 2 cm survey results caused by insufficient time sampling. These results emphasize the need for long time baselines and dense time sampling for multi-epoch monitoring of relativistic jets.

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