Images of M82 at 118 MHz (upper panel) and 154 MHz (lower panel) made using LOFAR baselines of length between 2 kλ and 60 kλ (robust 0 weighting). At 118 MHz the synthesised PSF (beam) is 5.79′′ × 4.53′′ and the rms noise is σ₁₁₈ = 0.50 mJy / beam. At 154 MHz the PSF is 4.66′′ × 3.56′′ and the rms noise is σ₁₅₄ = 0.27 mJy / beam. For deconvolution parameters, see Sect. 3.2. These images show the structure of the extended emission in grey scale (with brightness per respective beam size). The upper panel contours are drawn at (− 10,10,20,40,80,200,300) × σ₁₁₈ and the lower panel contours are (− 10,10,20,40,80,160,320,500) × σ₁₅₄. The symbols mark the positions of the sources listed in Table 2. The stars mark the power law-spectrum objects, shown in Fig. 5. The circles mark the turnover-spectrum objects, shown in Fig. 6. The plus signs mark the remaining objects listed in Table 2. Positions are given relative to the M82 position in Table 1.