2. Observations and data reduction

The objects observed were selected from Paper I and so we refer to that paper for the selection criteria. However, there are a few exceptions. Three objects (0120+33, 0800+24, 1339+26) in the sample of Paper I were not observed because of their low brightness. Two others, 1204+34 and 0836+29I, were not observed because of scheduling problems, and 1358+30 is no longer part of the sample (see Parma et al. 1996b, for more details on this object). On the other hand, we have observed 1511+26 that was not included in Paper I.

For some objects, 6 cm data were already available in the literature. Five objects (0206+35, 1113+29, 1553+29, 2116+26 and 2236+35) were presented in Morganti et al. (1987). However, these data have been re-analysed here to get an estimate of polarized intensity and fractional polarization consistent with the other objects. For three more objects (0844+31, 0836+29II and 1521+28) 6 cm data were presented in Capetti et al. (1995).

The observations at 6 cm were carried out, in most cases, by using the proper array to match the resolution of the previous 20 cm observations (e.g. B-array 20 cm/C-array 6 cm or C-array 20 cm/D-array 6 cm).

A log of the observations is given in Table 1 (click here). Each object was observed for about 1h at 4885 MHz with a bandwidth of 50 MHz. The beams and rms noises of the resulting maps are listed in Table 2 (click here).

 

Date Array

13 & 19 MAR92 array C

02AUG92 array D

28MAR93 array B

Table 1: Log of the observations

 

 

Object Beam

mJy/beam mJy/beam arcsec degree

0034+25 0.025 0.027 -10.8

0755+37 0.120 0.045 -73.8

0828+32 0.070 0.048 29.8

0913+38 0.036 0.030 -47.6

0915+32 0.065 0.047 16.6

0922+36 0.130 0.036 -12.4

1005+28 0.035 0.024 -21.4

1102+30 0.065 0.035 -10.9

1116+28 0.043 0.035 -44.6

1141+47 0.100 0.043 -45.9

1243+26 0.046 0.025 29.8

1300+32 0.040 0.030 -47.6

1316+29 0.100 0.047 -47.8

1357+28 0.040 0.037 12.4

1422+26 0.130 0.036 -74.5

1441+26 0.030 0.032 -83.9

1455+28 0.120 0.037 89.9

1528+29 0.027 0.025 27.0

1643+27 0.045 0.041 -86.6

1657+32 0.045 0.040 86.3

1658+30 0.085 0.046 77.9

1658+32 0.078 0.053 72.8

1752+32 0.045 0.040 68.1

1827+32 0.040 0.025 73.9

Table 2: D Array observations

 

 

Object Beam

mJy/beam mJy/beam arcsec degree

0149+35 0.040 0.029 12.1

0838+32 0.045 0.034 12.3

1108+27 0.037 0.025 7.3

1122+39 0.036 0.033 -16.2

1254+27 0.032 0.032 -15.1

1322+36 0.060 0.035 16.2

1347+28 0.027 0.025 -39.5

1430+25 0.033 0.033 -31.8

1450+28 0.030 0.030 -29.2

1457+29 0.032 0.023 -44.3

1512+30 0.025 0.022 -54.2

1511+26 0.050 0.036 -39.7

1527+30 0.040 0.034 -43.9

1553+29 0.033 0.030 -58.1

1609+31 0.036 0.034 -38.8

1613+27 0.035 0.039 -37.4

1615+32 0.127 0.045 -66.8

1626+39 0.080 0.045 -65.4

1726+31 0.083 0.055 -79.5

1747+30 0.039 0.034 -65.5

1833+32 0.600 0.100 -20.8

Table 2: continued, C array observations

 

Object Beam

mJy/beam mJy/beam arcsec degree

0708+32 0.045 0.041 18.5

0722+30 0.032 0.030 6.9

0908+37 0.040 0.040 -37.9

1003+26 0.032 0.031 9.9

1204+24 0.053 0.045 24.1

1303+31 0.061 0.034 20.1

1317+33 0.042 0.042 16.5

1525+29 0.048 0.037 23.9

1621+38 0.063 0.036 20.5

1855+37 0.073 0.038 5.6

Table 2: continued, B array observations

 

Object References

0206+35 Morganti et al. 1987

0836+29II Capetti et al. 1995

0844+29 Capetti et al. 1995

1113+29 Morganti et al. 1987

1521+28 Capetti et al. 1995

1553+29 Morganti et al. 1987

2116+26 Morganti et al. 1987

2236+35 Morganti et al. 1987

Table 2: continued, data from literature

Calibration and post-calibration reduction was done using the National Radio Astronomy Observatory (NRAO) AIPS package. The flux densities were brought on the scale of Baars et al. (1977) using 3C 286 and 3C 48 as primary flux calibrators. Polarization angles were measured relative to those of 3C 286 and 3C 138 and, by observing a secondary calibrator at enough parallactic angles, we were able to estimate a good solution for the instrumental polarization calibration ().

Maps of the Stokes parameters I, Q and U were produced for each source. Maps of the polarized flux density p=(Q²+U²)^1/2 and position angle were then obtained.

For each source we have estimated the integrated value of I, Q, U and p by using only the points that in the I maps have signal-to-noise ratios , following the same procedure described in Paper I. Using these values, we have derived both the vector mean fractional polarization () and the associated position angle A and the mean fractional polarization () with their associated errors. More details about these calculations are given in Paper I.