Calibration of Low-Frequency, Wide-Field Radio Interferometers Using Delay/Delay-Rate Filtering

TL;DR

This paper introduces a Fourier-based filtering method for selecting calibration sources in wide-field radio interferometry data, improving calibration accuracy despite RFI challenges.

Contribution

The paper presents a novel delay/delay-rate filtering technique and a CLEAN algorithm to enhance source selection and calibration in low-frequency, wide-field radio interferometers.

Findings

Effective source selection in delay/delay-rate images.

Successful calibration of PAPER data using the proposed methods.

Robustness against RFI excision effects.

Abstract

We present a filtering technique that can be applied to individual baselines of wide-bandwidth, wide-field interferometric data to geometrically select regions on the celestial sphere that contain primary calibration sources. The technique relies on the Fourier transformation of wide-band frequency spectra from a given baseline to obtain one-dimensional "delay images", and then the transformation of a time-series of delay images to obtain two-dimensional "delay/delay-rate images." Source selection is possible in these images given appropriate combinations of baseline, bandwidth, integration time and source location. Strong and persistent radio frequency interference (RFI) limits the effectiveness of this source selection owing to the removal of data by RFI excision algorithms. A one-dimensional, complex CLEAN algorithm has been developed to compensate for RFI-excision effects. This approach allows CLEANed, source-isolated data to be used to isolate bandpass and primary beam gain functions. These techniques are applied to data from the Precision Array for Probing the Epoch of Reionization (PAPER) as a demonstration of their value in calibrating a new generation of low-frequency radio interferometers with wide relative bandwidths and large fields-of-view.