We present radio continuum and linear polarisation observations of the pulsar wind nebula CTB 87 ( G 74.9 + 1.2 ) with the Effelsberg 100-m radio telescope between 4.75 and 32 GHz .
An analysis of these new data including archived low-frequency observations at 1420 MHz and 408 MHz from the Canadian Galactic Plane Survey shows that CTB 87 consists of two distinct emission components : a compact kidney-shaped component , 14 pc \times 8.5 pc ( 7 \farcm 8 \times 4 \farcm 8 ) in size and a larger diffuse , spherical and centrally peaked component of about 30 pc ( 17 \arcmin ) in diameter .
The kidney-shaped component with a much steeper radio continuum spectrum is highly linearly polarised and likely represents a relic pulsar wind nebula .
The diffuse component represents the undisturbed part of the PWN expanding inside a cavity or stellar wind bubble .
The previously reported spectral break above 10 GHz is likely the result of missing large-scale emission and insufficient sensitivity of the high-frequency radio continuum observations .
The simulation of the system ’ s evolution yields an age of about 18,000 years as the result of a type II supernova explosion with an ejecta mass of about 12 M _ { \odot } and an explosion energy of about 7 \times 10 ^ { 50 } erg .
We also found evidence for a radio shell in our polarisation data which represents the blast wave that entered the molecular cloud complex at a radius of about 13 pc .