The LOFAR Two-metre Sky Survey (LoTSS) VII. Third data release (HP-255)

The individual pointing images (at 6′′ and 20′′ resolution) were derived from 12,950 hrs (18.6 PB) of LOFAR High Band Antenna data which were processed through fully automated direction-independent and direction-dependent calibration pipelines that correct for instrumental effects as well as spatially and temporally varying ionospheric distortions.

The Stokes I images were then combined, accounting for the rms noise level and telescope beam, to form the final Stokes I mosaic images at 6′′ and 20′′ resolution, with a central frequency of 144MHz. From the 6′′ resolution Stokes mosaics we derived a catalogue of 13,664,379 radio sources (consisting of 16,943,656 Gaussian components), the majority of which have never been detected at radio wavelengths before. These mosaics have a median rms sensitivity of 92 μ Jy/beam; a random and systematic flux density scale accuracy of approximately 6% and 2%, respectively; an astrometric accuracy of 0.24′′; and we estimate that we detect more than 95% of sources with integrated flux densities exceeding nine times the local root mean square noise.