What material generates the hot gas responsible for the long-lasting thermal X-ray emission?
Answer
The shocked gas of the Interstellar Medium (ISM)
The X-ray glow is generated by the hot, shocked gas resulting from the blast wave slamming into the surrounding Interstellar Medium, which is distinct from the material powering the initial optical emission.

Related Questions
What powers the initial, prolonged optical glow of a supernova remnant for months to years?What element does Nickel-56 ($^{56} ext{Ni}$) primarily decay into?What physical process primarily generates the X-ray emission observed in supernova remnants?What mechanism is responsible for the distinctive, broad-spectrum radio emission from SNRs?Charged particles accelerated to extremely high energies within SNRs are known as what?What is the believed mechanism for accelerating particles within SNRs to generate cosmic rays?How is the amount of synthesized Nickel-56 ($^{56} ext{Ni}$) related to the supernova observation?What material generates the hot gas responsible for the long-lasting thermal X-ray emission?As a remnant ages, which emission phase eventually dwarfs the initial signal driven by radioactive decay?What specific characteristic derived from the X-ray spectrum informs astronomers about the shock wave?