Design, operation and performance of the PAON4 prototype transit interferometer

TL;DR

PAON4 is a prototype transit-mode interferometer with four dishes designed for intensity mapping of the 21cm hydrogen line, demonstrating key design features and performance metrics for large-scale structure surveys.

Contribution

This paper introduces the PAON4 prototype, detailing its design, operation, and performance, as a step toward large-scale structure mapping using radio interferometry.

Findings

PAON4 successfully operated over several years, providing valuable data for performance assessment.

Preliminary analysis shows stable calibration and noise characteristics.

The instrument demonstrates feasibility for intensity mapping of the 21cm line.

Abstract

PAON4 is an L-band (1250-1500 MHz) small interferometer operating in transit mode deployed at the Nan\c{c}ay observatory in France, designed as a prototype instrument for Intensity Mapping. It features four 5~meter diameter dishes in a compact triangular configuration, with a total geometric collecting area of $\sim75 \mathrm{m^2}$, and equipped with dual polarization receivers. A total of 36 visibilities are computed from the 8 independent RF signals by the software correlator over the full 250~MHz RF band. The array operates in transit mode, with the dishes pointed toward a fixed declination, while the sky drifts across the instrument. Sky maps for each frequency channel are then reconstructed by combining the time-dependent visibilities from the different baselines observed at different declinations. This paper presents an overview of the PAON4 instrument design and goals, as a prototype for dish arrays to map the Large Scale Structure in radio, using intensity mapping of the atomic hydrogen $21~\mathrm{cm}$ line. We operated PAON4 over several years and use data from observations in different periods to assess the array performance. We present preliminary analysis of a large fraction of this data and discuss crucial issues for this type of instrument, such as the calibration strategy, instrument response stability, and noise behaviour.