These, in turn, appear to have been made from some sort of false-color originals and most certainly are NOT accurate indications of intensity. The supernova remnant Cas A, in the Cassiopea constellation. The remnant is the result of a supernova explosion which occurred in our galaxy circa 1670 AD or about 320 year ago. The X-ray images represent a hot plasma cloud of several million degrees in temperatue produced when the blast wave from the supernova expands and heats the surrounding interstellar material. The remnant is located about 9,000-10,000 light years from Earth.
Galaxy clusters are traditionally strong X-ray emitters.
These gsas are typically tens of millions of degrees in temperature.