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Astron. Astrophys. 325, 911-914 (1997)

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2. Observations and data reduction

We present here a subset of the VLA A-array data at L and X bands and of the B-array at L band showing the polarization properties of six sources (Table 1). These have been selected among the observed objects as those clearly showing a polarized jet.


Table 1. Columns 1 through 6 show: source name, redshift, radio power at 1.4 GHz of the extended emission, percentage of polarization and E-vector position angle in the extended emission (typical errors of 0.1 - 0.2 % and 3 degrees), position angle of the projected magnetic field with respect to the direction of the jet (errors are around 5-10 degrees). The position where the polarization parameters are calculated is shown with a cross in each image and corresponds to the location of the maximum brightness of polarized emission out of the nucleus. The frequency and array configuration at which the quantities presented here are derived for each object is indicated in the caption of the corresponding figure. The redshift of 1147+245 is unknown; the median value for the redshift distribution of the 1 Jy sample has been used for this object.

The data reduction has been done in the standard way using the NRAO Astronomical Image Processing System (AIPS). We used 3C286 to calibrate the absolute flux density scale according to the value given by Baars et al. (1977). The radio source 3C286 has been also used to calibrate the polarization position angle. Several iterations of phase self-calibration followed by a final step of amplitude and phase self-calibration were performed to correct for antenna based errors, until the process converged to a stable solution. With this procedure we were able to achieve an rms noise on the cleaned images close to the expected thermal noise. Correction for baseline based errors was not necessary. The polarization images were corrected for the positive bias arising from the Ricean noise.

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© European Southern Observatory (ESO) 1997

Online publication: April 28, 1998