Introduction

In this section we explain about the actual observing setup used and the observational procedure for the calibrator observation at the GMRT. All the observations were done in the dual frequency (610 MHz & 235 MHz) mode. Among the frequency bands used in the GMRT, 610 MHz/235 MHz have been designed as a co-axial horn pair. Hence they can be used simultaneously and it gives 610 MHz in one polarization channel and 235 MHz in other.

The measured system parameters of GMRT for 610 MHz and 235 MHz are given below. These parameters are used mainly to find out the theoretical $rms$ of the map.

• Primary beam for 610 MHz is 43$\pm$3 arc-minute and for 235 MHz is 114$\pm$5 arc-minute.
• Total system temperature for 610 MHz is 92 K and for 235 MHz is 177 K.
• Synthesized Beam for whole array for 610 MHz is 5 arc-seconds and for 235 MHz is 13 arc-seconds.

The observations were done in Nov-Dec 2003 and Mar-Apr 2005. The observing time was alloted during the system-test time of the GMRT or during the white-slot (intentional spare time) of GTAC (GMRT Time Allocation Committee) Schedule by the Center Director, NCRA. A few sources for which data were badly corrupted during the the first observing run, i.e. in Nov-Dec 2003 were re-observed along with the remaining sources in the list during the Mar-Apr 2005 observing run.