Abstract Details

Name: Surajit Mondal
Affiliation: National Center for Radio Astrophysics
Conference ID: ASI2017_1290
Title : Full-Stokes Holographic Measurement of GMRT Primary Beams
Authors and Co-Authors : Surajit Mondal(NCRA, TIFR), Niruj R. Mohan (NCRA, TIFR), Divya Oberoi(NCRA, TIFR), Santaji Katore (NCRA, TIFR)
Abstract Type : Oral
Abstract Category : Instrumentation and Techniques
Abstract : The primary beam of individual antennas serves as an envelope for the response of a radio interferometer. Traditionally it is assumed that all the antennas have identical and azimuthally symmetric primary beams, which allows us to apply a single multiplicative correction to the final image. In reality, the primary beam for the GMRT, like any other interferometer, has significant departures from azimuthal symmetry and also varies from antenna to antenna. In addition, the alt-az mount of the GMRT makes this beam rotate with time while tracking a source. These effects result in time and direction dependent gains for each antenna. Left uncorrected, this limits the dynamic range of the final image and this problem is exacerbated with the increased sensitivity of the GMRT. Software that is able to correct for time and antenna dependent primary beams are being developed only now. In order to achieve the theoretical sensitivity in deep wide-field images made with the uGMRT, it is essential to account for these effects. We have therefore embarked on an exercise to measure the vector primary beams of all the GMRT antennas in all the 4 Stokes parameters at all frequency bands. Here, we discuss the methodology adopted and present initial results from this project.