Imaging sensitivity of a linear interferometer array on lunar orbit

TL;DR

This paper evaluates the imaging sensitivity and quality of a lunar orbit interferometer array designed to observe low-frequency radio waves, proposing new data-processing methods and estimating its potential to detect hundreds to tens of thousands of sources.

Contribution

It introduces a simulation-based assessment of a lunar orbit interferometer array's imaging capabilities and sensitivity, including practical estimates of source detection potential.

Findings

Array can achieve good angular resolution despite small antennas.

Estimated detection of 100 to 10,000 sources depending on source distribution.

Developed new data-processing methods for lunar orbit interferometry.

Abstract

Ground-based observation at frequencies below 30 MHz is hindered by the ionosphere of the Earth and radio frequency interference. To map the sky at these low frequencies, we have proposed the Discovering the Sky at the Longest wavelength mission (DSL, also known as the "Hongmeng" mission, which means "Primordial Universe" in Chinese) concept, which employs a linear array of micro-satellites orbiting the Moon. Such an array can be deployed to the lunar orbit by a single rocket launch, and it can make interferometric observations achieving good angular resolutions despite the small size of the antennas. However, it differs from the conventional ground-based interferometer array or even the previous orbital interferometers in many aspects, new data-processing methods need to be developed. In this work, we make a series of simulations to assess the imaging quality and sensitivity of such an array. We start with an input sky model and a simple orbit model, generate mock interferometric visibilities, and then reconstruct the sky map. We consider various observational effects and practical issues, such as the system noise, antenna response, and Moon blockage. Based on the quality of the recovered image, we quantify the imaging capability of the array for different satellite numbers and array configurations. For the first time, we make practical estimates of the point source sensitivity for such a lunar orbit array, and predict the expected number of detectable sources for the mission. Depending on the radio source number distribution which is still very uncertain at these frequencies, the proposed mission can detect $10^2 \sim 10^4$ sources during its operation.