As a remnant ages, which emission phase eventually dwarfs the initial signal driven by radioactive decay?

Answer

The shock-driven signals (X-ray and radio)

As the shock wave propagates, the input of thermal energy from the expanding debris eventually surpasses the fading energy from atomic breakdown, causing the X-ray and radio signatures to take over as the primary visible 'glow'.

As a remnant ages, which emission phase eventually dwarfs the initial signal driven by radioactive decay?
astronomyradiationsupernovaastrophysicsremnantssupernovae