The Fourier inversion of the gain calibrated visibility data of target source was performed by the AIPS task IMAGR. The task has multi-capabilities like application of data calibration for source data sets, data sorting if needed to fit the weighting, griding or CLEANing, data imaging in up to 4096 simultaneous facets, CLEANing all the fields simultaneously with subtraction of CLEAN components form the data of each major cycle followed by re-computation of the residual images, avoiding aliasing of side-lobes and allowing components almost to the edges of each field, re-projection of the (u,v,w) baseline coordinates to make each field tangent to the Celestial sphere at its center thereby making a larger area of each field free of projection defects, correction of CLEAN components for various wide-field and wide-bandwidth effects, truly interactive TV display of residual images allowing one to alter the areas over which CLEAN components are sought, sensible CLEANing strategies for, and restoration to, overlapped image fields, etc.
Since we have data for two frequencies viz. 610 MHz & 235 MHz, and the data at low radio frequencies i.e at 235 MHz, suffer from w-term effects, we followed different procedure to process the data at these two frequencies. The procedure followed in the AIPS task IMAGR at 610 MHz and 235 MHz is described below. The settings of relevant verbs and adverbs within the task are also discussed.
Our Methodology and use of AIPS