It is possibly the brightest diffuse nebula visible to the naked eye in the night sky.
From the en.wikipedia.org
This same supernova's remains can be seen today as the Crab nebula, a diffuse, glowing gas cloud 3,500 light years away, which continues to expand at 800 miles per second.
From the time.com
The diffuse fringes of the nebula prevent the energetic outflows from streaming directly away from the cluster, leaving instead a trail of filaments marking the swirling path of the outflows.
From the sciencedaily.com
What you'd look for is faint and diffuse X-ray emission, and you'd see how far it extends around the interior regions of the nebula.