Origin of position-dependent flux density scale variations in individual LoTSS pointings

Determine the physical and calibration origins of the position-dependent variations in the integrated flux density scale across the field of view in individual LOFAR Two-metre Sky Survey (LoTSS) High Band Antenna 120–168 MHz pointing images, and quantify the contribution of LOFAR primary beam model inaccuracies to these variations so that robust, uniform flux calibration can be achieved across each pointing.

Background

The LoTSS-DR3 team observes that the integrated flux density scale varies across the field of view of individual pointings. While they implemented an empirical correction by fitting position-dependent planes to align neighboring fields, the root cause of these spatial variations is not established.

They note that errors in the LOFAR primary beam model may contribute. Understanding the origin is important for improving calibration accuracy and ensuring uniformity of the flux density scale across the survey, which affects downstream scientific analyses such as source counts and spectral studies.

References

As is shown in Fig. 9 of , the integrated flux density scale varies across the field of view of individual LoTSS pointings. The origin of this variation is not yet fully understood, although it is thought that errors in the current LOFAR beam model may play a role.

— The LOFAR Two-metre Sky Survey: VII. Third Data Release  (2602.15949 - Shimwell et al., 17 Feb 2026) in Section 3.2 (Flux density scale refinement)