SIMBAD references

In this paper we describe a method for measuring the effective receiver temperature T_erc and its variation for the entire receiver chain of a radio telescope, and use it to make a radio-continuum map of the sky at 240MHz using the Giant Metrewave Radio Telescope (GMRT). We also show that in the case of GMRT, T_erc varies mainly with elevation and ambient temperature. The calibration techniques evolved here are applicable to similar interferometers with a large number of antennas, several frequency bands and a number of receiver systems at room temperature (where conventional methods are time-consuming). This method ideally requires just one complete day of observations in a frequency band.