The image is a little weird because it's a composite involving two radio images, both from around 1.5 GHz: a lower-resolution image taken by the Canadian Galactic Plane Survey (~1.42 GHz) and a higher-resolution one taken by the Very Large Array (~1.5 GHz), along with infrared imaging from IRAS (in blue). There's a nice gif showing the difference; the CGPS image is held static and the VLA image fades and then disappears:
Image credit: Composite by Jayanne English, University of Manitoba; F. Schinzel et al.; NRAO/AUI/NSF; DRAO/Canadian Galactic Plane Survey; and NASA/IRAS.
Let's talk about what this shows:
- The crescent-shaped arc shows the edge of the expanding supernova remnant as it collides with the interstellar medium. As the ejecta moves through the ISM, the resulting shock waves heat it up, leading to emission. Since the pulsar has been kicked at a significant speed, there's probably asymmetry to the remnant (although inhomogeneities in the ISM can also lead to asymmetry). The darkness in the center is likely not a shadow but rather the result of how an observer's lines of site pass through the nebula — similar to the appearance of planetary nebulae.
- The line does indeed trace the path of the pulsar through space. As discussed in the paper from the VLA observations (Schinzel et al. 2019), the shape and spectrum of that region of radio emission point to (non-thermal) synchrotron emission from a bow shock. Basically, as the pulsar moves through the interstellar medium, its wind of energetic particles gets compressed and shocked from ram pressure — again, the result of something moving very quickly through the ISM.
- I'm not positive what the other blobs are. Some are certainly stars; because of the low resolution of the CGPS image, though, I can't say for sure that all of them are.
- All of the above features show up in the radio images, in orange. Although it's not explicitly stated anywhere, I believe the blue is infrared IRAS data. Much of it also traces the shape of remnant, hidden behind the CGPS data, although the blobs at bottom left and upper right are likely unrelated features, probably something ISM-ish.
The bottom line is that it's all really just hot stuff glowing.