Tapering the sky response for angular power spectrum estimation from low-frequency radio-interferometric data

TL;DR

This paper introduces a method to improve the estimation of the diffuse sky signal's power spectrum in low-frequency radio interferometry by tapering the sky response, reducing point source contamination especially at the edges.

Contribution

The paper presents a novel tapering technique combined with the Tapered Gridded Estimator to effectively suppress outer point sources and accurately estimate the angular power spectrum from simulated data.

Findings

Successfully suppresses outer point source contributions

Accurately computes and subtracts noise bias

Provides unbiased power spectrum estimates

Abstract

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 center. 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 spectrum C_l of 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 of C_l.