Tapering the sky response for angular power spectrum estimation from low-frequency radio-interferometric data.
It is important to correctly subtract point sources from radio-interferometric data in order to measure the power spectrum of diffuse radiation like the Galactic synchrotron or the Epoch of Reionization 21-cm signal. It is computationally very expensive and challenging to image a very large area and accurately subtract all the point sources from the image. The problem is particularly severe at the sidelobes and the outer parts of the main lobe where the antenna response is highly frequency dependent and the calibration also differs from that of the phase centre. Here, we show that it is possible to overcome this problem by tapering the sky response. Using simulated 150 MHz observations, we demonstrate that it is possible to suppress the contribution due to point sources from the outer parts by using the Tapered Gridded Estimator to measure the angular power spectrumCℓof the sky signal. We also show from the simulation that this method can self-consistently compute the noise bias and accurately subtract it to provide an unbiased estimation ofCℓ.
Department of Physics, Centre for Theoretical Studies, IIT Kharagpur, Kharagpur 721 302, India.
Samir
S
Choudhuri
Department of Physics, Centre for Theoretical Studies, IIT Kharagpur, Kharagpur 721 302, India.
Somnath
S
Bharadwaj
Department of Physics, Centre for Theoretical Studies, IIT Kharagpur, Kharagpur 721 302, India.
Nirupam
N
Roy
Kapteyn Astronomical Institute, PO Box 800, NL-9700 AV Groningen, the Netherlands.
Abhik
A
Ghosh
Department of Physics, Jadavpur University, Kolkata 700032, India.
Sk Saiyad
SS
Ali
diffuse radiation; methods: data analysis; methods: statistical; techniques: interferometric