A decade of sub-arcsecond imaging with the International LOFAR Telescope

TL;DR

The paper reviews a decade of sub-arcsecond imaging with the International LOFAR Telescope, highlighting technical advances, scientific capabilities, and ongoing projects that leverage its high-resolution low-frequency radio observations.

Contribution

It provides a comprehensive overview of the technical methods, calibration, and scientific applications of sub-arcsecond imaging with ILT, emphasizing its unique capabilities and future directions.

Findings

Increased publication output due to accessible imaging pipeline.

ILT's resolution and frequency range enable diverse scientific studies.

Ongoing projects include large-area surveys and deeper, lower-frequency imaging.

Abstract

The International LOFAR Telescope (ILT) is a pan-European radio interferometer with baselines up to 2,000 km. This provides sub-arcsecond resolution at frequencies of <200 MHz. Since starting science operations in 2012, the ILT has carried out observations for the state-of-the-art LOFAR Two-metre Sky Survey, which has 6 arcsec resolution at 144 MHz. Wide-area surveys at low frequencies, while scientifically productive, have to compromise on resolution. Sub-arcsecond imaging with the ILT has become more accessible over the last decade, thanks to efforts to build a publicly available pipeline using LOFAR-specific tools, which has resulted in a dramatic increase in the number of publications. The ILT's combination of resolution, field of view, and low observing frequency make it a unique instrument for a wide range of scientific applications, and it will remain unparalleled even in the era of the Square Kilometre Array Observatory. Here we provide an overview of the technical considerations and calibration methods sub-arcsecond imaging with the ILT. This is followed by a review of the unique capabilities unlocked by sub-arcsecond imaging with the ILT, using examples from the literature for demonstration. Finally we describe ongoing work including: surveying large areas of the sky at high resolution, going deeper in fields with excellent ancillary information, producing images of polarisation, and extending to lower frequencies (<100 MHz).