2025A&A...704A..65B

Context. The Low Frequency Array (LOFAR) is uniquely able to perform deep, 15" resolution imaging at frequencies below 100 MHz. Observations in this regime, using the Low Band Antenna (LBA) system, are significantly affected by instrumental and ionospheric distortions. Recent developments in calibration techniques have enabled the routine production of high-fidelity images at these challenging frequencies.
Aims. The aim of this study was to obtain images of the radio sources included in the Third Cambridge catalog, second revised version (3CRR), at an observing frequency of 58 MHz, with an angular resolution of 15" and sensitivity to both compact and diffuse radio emission. This work also aimed to produce accurate flux measurements for all sources. This dataset is designed to serve as a reference for low-frequency radio galaxy studies and future spectral aging analyses.
Methods. We present the data reduction and calibration procedures developed for narrowband observations of bright sources with the LOFAR LBA. These include tailored direction-independent calibration strategies optimized for mitigating ionospheric phase corruptions and instrumental effects at 58 MHz. Imaging techniques were refined to reliably recover both small- and large-scale radio structures reliably.
Results. We deliver 58 MHz radio images that include flux density measurements for the complete 3CRR sample. We determine that the LBA has an accurate flux density scale with an average flux uncertainty of 10%. This is an important confirmation for any future works using the LOFAR LBA system. With these results, we characterized the bright radio galaxy population with new high-resolution low-frequency images. We also provide high-resolution models of these sources, which will be useful for calibrating future surveys.
Conclusions. This legacy survey significantly expands the available high-resolution data at low frequencies and is the first fully imaged high-resolution sample at ultra-low frequencies (<100 MHz). It lays the foundation for future studies of radio galaxy physics, low-energy cosmic-ray populations, and the interplay between radio jets and their environments.