610 MHz $--$ Our Methodology and use of AIPS

The visibility data data file obtained from the task SPLIT which are single source calibrated data files, were used as a input to the task IMAGR. The task IMAGR creates two files one is the beam file and other is the map file. Map files, if CLEANed, also contain the table of clean components descending value of the component flux.

We first made two sets of maps, a low resolution map to look for presence of any other strong source within the field-of-view and with this input information, later, the other high resolution map was made.

For low resolution map, i.e. with resolution of 10$^{''}$ (arc sec) with field of view of $\approx$ 52' (arc min), the parameters used were:
CELLSIZE = 3,3; IMSIZE=1024,1024; NFIELD=1; NITER=1000; GAIN=0.05; UVTAPER=15,15; DOTV=$-$1. Default values used for the remaining parameters. CELLSIZE is the pixel separation in arc second, IMSIZE is the size of the filed in pixels, NFIELD is the number of fields to map in the antenna beam, NITER is the maximum number of iteration in a process, such as CLEANing an image, GAIN is loop gain for CLEAN; this number will be multiplied by the peak in the residual map to determine the flux density of a CLEAN component to be removed, UVTAPER is to specify the widths in U and V directions of the Gaussian function, For DOTV the value was kept $-$1 to do a blind CLEANing.

In addition, a uniform weighting function was used to equalize coverage of measured points in $UV$ plane. In uniform weighting, weights are corrected for the local density of data weights.

For high resolution map, i.e. resolution of $\sim$ 3$^{''}$ (arc-second) with field of view $\approx$ 14' (arc min), the parameters used are:
CELLSIZE=0.8,0.8; IMSIZE=1024,1024; UVTAPER=0,0; DOTV=$-$1

The low resolution maps were used to note down information about the other strong source in the field like its flux density, its distance from the phase center and its position angle, etc. High resolution map is used for getting information, peak and integrated flux of the source, beam minor axis (in pixels), deconvolved major axis (in pixels) etc. This information is summarized in the next chapter 4.

The task JMFIT was used for getting the flux density information. It gives the information the fitted Gaussian components for the given portion of the image and it also solves for the constant, linear or quadratic two-dimensional 'baseline' surface.