65″ × 33″ difference image between NTT/EMMI/[O III]/0 and NTT/EMMI/[O III]/6000 with square root intensity scaling to bring out faint details. The [O III]/0 image was smoothed to match the slightly worse seeing of the [O III]/6000 image before subtraction. North is up and east is to the left. The image can trace faint [O III] emission to large distances from the pulsar. A blue circle is drawn with radius 100, corresponding to ∼ 2150 km s⁻¹ for ejecta coasting freely for 1100 years (or ∼ 1980 km s⁻¹ for 1200 years) at distance of 50 kpc. The filaments F1, F2, F4, and F5, discussed in the text, are marked. Note PWN protrusions to the north, presumably in the pulsar jet direction, and to the southwest, which could be a structure similar to the Crab chimney.