Color scale shows the intensity of the LOFAR image at 144 MHz and 19′′× 18′′ of resolution. Top panel shows a field of view of 5.8 × 5.8 deg2 (~ 2 times the primary beam). At the edge of the field, some sources suffer from bandwidth smearing. These problems are not seen in the bottom panel, which displays the 2 × 2 deg2 area that was used for the source count (Sect. 3.3).