2. Observations and reduction
2.1. (a) Geodetic VLBI data
We have used in this work 8 GHz geodetic data obtained with the Global VLBI Network at 8 epochs during the period from 1995.06 to 1996.68. All the data have been received from Goddard Space Flight Center. Calibration parameters necessary for conversion of the correlation coefficients into correlated flux densities were kindly provided by Dr. D.Shaffer. Mapping and model-fitting with elliptical gaussian components were performed with the Caltech VLBI Package software on a VAX634 computer.
2.2. (b) 22 and 43 GHz VLBA observations
We observed 0202+149 with the VLBA as a part of a -ray bright blazar monitoring compaign at 5 epochs between 1994.18 and 1997.58 at frequencies of 22 and 43 GHz. The observations were carried out with the VLBA recording system using four 8 MHz wide channels in both right and left circular polarization, in "snapshot" mode. The flux densities were calibrated using 22 and 37 GHz single-antenna measurements obtained at the Metsähovi Radio Research Station. Corrections were made for zenith opacities, antenna gain curves, and system temperatures (the latter two supplied by NRAO).
The Astronomical Image Processing System (AIPS) software was used for primary data reduction, while imaging and model fitting were performed as above but using the software Difmap (Shepherd 1997). The flux densities were adjusted a posteriori for discrepancies between the gain curves and actual antenna performance by requiring that the total fluxes on the images of nearly unresolved calibrating sources match the Metsähovi values.
© European Southern Observatory (ESO) 2000
Online publication: June 8, 2000