Astron. Astrophys. Suppl. Ser. 132, 261-273

Spectral distributions in compact radio sources

I. Imaging with VLBI data

A.P. Lobanov

Send offprint request: A.P. Lobanov

Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany

Received September 11, 1997; accepted April 4, 1998

Abstract:

We discuss a technique for mapping the synchrotron turnover frequency distribution using nearly simultaneous, multi-frequency VLBI observations. The limitations of the technique arising from limited spatial sampling and frequency coverage are investigated. The errors caused by uneven spatial sampling of typical multi-frequency VLBA datasets are estimated through numerical simulations, and are shown to be of the order of 10%, for pixels with the deconvolution ${\rm SNR} \sim 7$. The fitted spectral parameters are corrected for the errors due to limited frequency coverage of VLBI data. First results from mapping the turnover frequency distribution in 3C345 are presented.

Key words: methods: data analysis -- methods: observational -- quasars: individual: 3C345 -- techniques: interferometric