Plots - $uv$ Distance

We present plots of flux density (in Jy) as a function of $uv$-distance (in kilo wavelength) for the 610 MHz GMRT data.

The $uv$-distance plots are obtained using the AIPS task UVPLT, it was run on the single channel (averaged) uv-data file obtained from the task SPLAT. The task UVPLT was run using following parameters : DOCALIB=1; BCHAN=1; ECHAN=0; BPARM=0 0 1 0 0 0 3 10 1 0. DOCALIB=1 is to apply the calibration, BPARM(3)=1 is to put fixed scale for X & Y axis, BPARM(7)=3 is to change the Y axis maximum value to a desired value. This value has been changed for each plot as per the flux density of the source, BPARM(8)=10 is number of bins to be plotted, BPARM(9)=1 is for the values and standard deviations in each bin that will be put in the message file (prio=5). Note that this parameter has no effect if the plot is not binned.

In the table A.1, the last column gives comments based on the $uv$-distance plots. If the plot is flat over all the baseline lengths, or in other words, flux density is constant as a function of $uv$-distance (see the fig 4.1), it has been indicated as F in the table, and it should be considered as a good quality point source for these scales of baselines.

Figure 4.1: 'Flat' $uv$-distance plots of the sources at 610 MHz.

On the other hand, if the plot is not a flat function on all scales of baseline lengths and it shows the variation of flux density as a function of $uv$-distance more than $\approx$ 10-15% of the flux density of the source, has been marked as NF. There could be several reasons for this behavior, e.g, source is resolved on the observed $uv$ scales or the presence of strong source near the source, etc. and these sources are not recommended as calibrator sources.

At 610 MHz, among all the observed sources, larger fraction of sources showed a flat $uv$-distance plot. Out of 150 sources, 129 sources were classified as flat and 21 sources as non-flat. In fig 4.2, we present all 21 $uv$-distance plots of non-flat sources.

Figure 4.2: 'Non-Flat' $uv$-distance plots of the sources at 610 MHz.

Figure 4.2: 'Non-Flat' $uv$-distance plots of the sources at 610 MHz.

Figure 4.2: 'Non-Flat' $uv$-distance plots of the sources at 610 MHz.

Figure 4.2: 'Non-Flat' $uv$-distance plots of the sources at 610 MHz.